J Clin Oncol 30(4): 406-412

PMC: PMC3269966

PMID: 22203756

Association of Obesity With DNA Mismatch Repair Status and Clinical Outcome in Patients With Stage II or III Colon Carcinoma Participating in NCCTG and NSABP Adjuvant Chemotherapy Trials

Purpose

Although the importance of obesity in colon cancer risk and outcome is recognized, the association of body mass index (BMI) with DNA mismatch repair (MMR) status is unknown.

Patients and Methods

BMI (kg/m^{) was determined in patients with TNM stage II or III colon carcinomas (n = 2,693) who participated in randomized trials of adjuvant chemotherapy. The association of BMI with MMR status and survival was analyzed by logistic regression and Cox models, respectively.}

Results

Overall, 427 (16%) tumors showed deficient MMR (dMMR), and 630 patients (23%) were obese (BMI ≥ 30 kg/m^{). Obesity was significantly associated with younger age (}P = .021), distal tumor site (P = .012), and a lower rate of dMMR tumors (10% v 17%; P < .001) compared with normal weight. Obesity remained associated with lower rates of dMMR (odds ratio, 0.57; 95% CI, 0.41 to 0.79; P < .001) after adjusting for tumor site, stage, sex, and age. Among obese patients, rates of dMMR were lower in men compared with women (8% v 13%; P = .041). Obesity was associated with higher recurrence rates (P = .0034) and independently predicted worse disease-free survival (DFS; hazard ratio [HR], 1.37; 95% CI, 1.14 to 1.64; P = .0010) and overall survival (OS), whereas dMMR predicted better DFS (HR, 0.59; 95% CI, 0.47 to 0.74; P < .001) and OS. The favorable prognosis of dMMR was maintained in obese patients.

Conclusion

Colon cancers from obese patients are less likely to show dMMR, suggesting obesity-related differences in the pathogenesis of colon cancer. Although obesity was independently associated with adverse outcome, the favorable prognostic impact of dMMR was maintained among obese patients.

INTRODUCTION

Recent data suggest that molecular markers, including DNA mismatch repair (MMR) status, can be used to classify colorectal cancers (CRCs) into distinct subtypes, which has implications for etiology, prognosis, and treatment. MMR is involved in the etiology of CRC with approximately 10% to 20% of tumors¹ developing due to deficient function of this system, which gives rise to microsatellite instability (MSI).² Among tumors with deficient MMR (dMMR), approximately two thirds arise sporadically as a consequence of epigenetic inactivation of the MLH1 MMR gene¹,3 and the other nearly one third carry a germline MMR gene mutation (MLH1, MSH2, MSH6, PMS2) that confers Lynch syndrome.⁴ Tumors showing dMMR have a distinct phenotype that includes proximal site, poor differentiation, diploid DNA content, and abundant tumor infiltrating lymphocytes.²,5–8 Evidence indicates that MMR status confers prognostic information in patients with colon cancer⁶,9–13 and may also influence response to fluorouracil (FU) -based adjuvant chemotherapy.⁹,14–16 To date, however, only limited data exist regarding the association of MMR status with body mass index (BMI)¹⁷ or lifestyle factors¹⁸,19 in patients with colon cancer.

Obesity is an established risk factor for developing colon cancer, with the risk being stronger in men versus women,²⁰–25 and may be associated with increased mortality related to this malignancy.²⁶–28 Obesity is associated with increased circulating levels of estrogens in both men and women,²⁹ and evidence suggests that estrogen exposure may protect against the development of dMMR tumors.³⁰ Rates of obesity have increased two-fold in adults and three-fold in children in the past 30 years in the United States and are also rising in other parts of the developed world.³¹ Data from the National Health and Nutrition Examination Survey indicate that approximately 34% of US adults—almost 73 million people—are obese, defined by the WHO³² as having a BMI of ≥ 30 kg/m^.³³ In an effort to distinguish the impact of obesity from MMR status, which have both been shown to influence patient survival, we determined their association and compared patient outcomes in a large cohort of patients with stage II or III colon cancer who participated in phase III clinical trials of adjuvant chemotherapy. Determining the association of obesity with MMR status may also provide insight into the molecular pathogenesis of colon cancer and may identify a modifiable factor associated with the MMR phenotype.

PATIENTS AND METHODS

The study population consisted of patients (N = 2,693) with pathologically confirmed TNM stage II (n = 714) or III (n = 1,979) colonic adenocarcinomas who were participants in nine phase III randomized trials of adjuvant chemotherapy. Studies included those conducted by the Mayo Clinic/North Central Cancer Treatment Group (NCCTG) that evaluated FU with levamisole or leucovorin (LV) versus surgery alone (NCCTG 78-48-52³⁴,35 and NCCTG 84-46-52/Intergroup 0035 [INT 0035]³⁶,37). Other studies evaluated combinations of FU with levamisole and/or LV (NCCTG 89-46-51³⁸), FU with LV and interferon-gamma with or without levamisole (NCCTG 87-46-51³⁹), and FU plus LV with high versus standard dose levamisole (NCCTG 91-46-53⁴⁰). We also included studies conducted by the National Surgical Adjuvant Breast and Bowel Project (NSABP) that randomly assigned patients to portal venous FU versus surgery alone (NSABP C-02); FU, vincristine, and semustine versus FU plus LV (NSABP C-03); FU plus LV versus FU plus LV plus levamisole (NSABP C-04⁴¹); and FU plus LV and oxaliplatin versus FU plus LV (NSABP C-07⁴²). Within the study population, 1,759 received FU-based chemotherapy, and the remaining patients received non–FU-based treatment (n = 774) or surgery alone (n = 160).

Patient data were obtained from the cooperative group databases. Only patients with available tissue specimens were included. Tumor site was categorized as proximal when cancers were located above the splenic flexure and all other tumor sites were categorized as distal. Study patients were required to have a baseline Eastern Cooperative Oncology Group (ECOG) performance score of 0 to 2.⁴³ Written informed consent was obtained from all study participants, and protocols were approved by the institutional review boards at the respective study sites. This study was conducted under an active institutional review board–approved protocol.

Assessment of Patient BMI

By using patient height and weight data obtained and recorded at study entry, trained personnel calculated BMI by taking the body weight in kilograms divided by height in meters squared. These measurements were also used to calculate chemotherapy dosages. BMI was categorized as underweight (BMI, < 20 kg/m^{), normal weight (BMI, 20.1 to 24.9 kg/m}^{), overweight (BMI, 25 to 29.9 kg/m}^{), or obese (BMI, ≥ 30 kg/m}^{) according to WHO criteria.}³²

Assessment of Tumor MMR Status

MMR status was determined by analysis of MSI and/or MMR protein expression by immunohistochemistry (IHC). dMMR was defined as MSI high frequency (MSI-H) or loss of expression of an MMR protein by IHC. Proficient MMR (pMMR) was defined as MSI low frequency (MSI-L) or microsatellite stable (MSS) or as intact expression of all MMR proteins evaluated.

MSI testing.

MSI was analyzed by polymerase chain reaction amplification of microsatellite loci in microdissected, tumor-enriched paraffin-embedded tissue. Specimens from NCCTG studies were screened by using four to 11 microsatellite markers, as previously described.¹¹,44 In NCCTG 91-46-53, MMR status was determined by analysis of instability at BAT26 coupled with MLH1, MSH2, and MSH6 protein expression.⁴⁰ Within NSABP studies, MSI was analyzed by using the marker panel recommended by the National Cancer Institute (BAT25, BAT26, D5S346, D2S123, and D17S250)⁴⁵ and the transforming growth factor-beta type II receptor locus.⁴¹ Tumors were classified as MSI-H if ≥ 30% of the markers demonstrated instability, as MSI-L if more than 0% and less than 30% showed MSI, and as MSS if none of the markers exhibited MSI.⁴⁵

IHC analysis of MMR proteins.

Paraffin-embedded tumor sections were analyzed for MLH1 and MSH2 proteins, as previously described.⁴⁶ Staining was performed by using primary monoclonal antibodies: mouse antihuman MLH1 (clone G168-728, 1:250; BD Pharmingen, San Diego, CA) and mouse antihuman MSH2 (clone FE11, 1:50; Oncogene Research Products, Cambridge, MA). MSH6 was analyzed by using a mouse antihuman MSH6 monoclonal antibody (clone 44; Transduction Laboratories, Lexington, KY) in tumors (n = 387) from one study (NCCTG 91-46-53). Loss of an MMR protein was defined as absence of nuclear staining of tumor cells in the presence of positive nuclear staining in normal colonic epithelium and lymphocytes. Each slide was assigned a unique number that enabled blinding to patient identity and clinical characteristics.

Statistical Analysis

The χ^{or Cochran-Armitage trend test was used to measure the association between BMI and categorical clinicopathologic variables. The Kruskal-Wallis or Wilcoxon rank sum tests were used for continuous variables. Univariate and multivariate logistic regression models were used to test for the association between obesity and MMR status after stratifying by study. Odds ratios and 95% CIs were calculated. Overall survival (OS; censored at 8 years) was calculated as the number of years from random assignment to date of death or last contact. Disease-free survival (DFS; censored at 5 years) was calculated as number of years from random assignment to first of either disease recurrence or death. The association of BMI and covariates with DFS and OS were determined by using Kaplan-Meier methodology and Cox proportional hazards models.}⁴⁷ Score and likelihood ratio tests were used to evaluate the significance of each covariate in univariate and multivariate models, respectively, after stratifying by treatment and study. Statistical tests were two-sided, with P ≤ .05 considered significant. All analyses were performed by using SAS software (SAS Institute, Cary, NC).

Assessment of Patient BMI

Assessment of Tumor MMR Status

MSI testing.

IHC analysis of MMR proteins.

MSI testing.

IHC analysis of MMR proteins.

Statistical Analysis

RESULTS

Patient Characteristics by MMR Status and BMI Category

Of the 2,693 patients, 714 (26.5%) had stage II and 1,979 (73.5%) had stage III colon carcinomas that had been resected with curative intent. MMR status was determined in all patients, and dMMR was detected in 427 patients (16%) with cancer. A higher rate of dMMR was found in stage II (178 of 714; 25%) versus stage III (249 of 1,979; 13%) cancers (P < .001) and in women compared with men (18% v 14%; P = .0037). When age was dichotomized at 50 years as an indicator of menopausal status, a higher rate of dMMR was found in older versus younger women (20% v 12%; P = .0025).

Among all patients, 630 (23%) were obese (BMI ≥ 30 kg/m^{), 1,042 (39%) were overweight (BMI 25 to 29.9 kg/m}^{), 879 (33%) were of normal weight (BMI 20 to 24.9 kg/m}^{), and 142 (5%) were underweight (BMI < 20 kg/m}^{). Demographic and clinicopathologic features of the study population were stratified by BMI category (}Table 1). Across all BMI categories, statistically significant differences were observed for patient age, sex, tumor site, histologic grade, and MMR status (Table 1). Compared with those of normal weight, obese patients were significantly more likely to be younger and to have tumors located in the distal (v proximal) colon with low (v high) histologic grade. Obese patients had a dMMR rate of 10.3% that was significantly lower than the dMMR rates of 17.1%, 17.4%, and 21.8% in overweight, normal weight (Fig 1A), and underweight BMI categories, respectively (P < .001; Table 1). Moreover, obesity remained significantly associated with lower rates of dMMR (odds ratio, 0.57; 95% CI, 0.41 to 0.79; P < .001), after adjusting for factors known to be associated with MMR status (ie, tumor site, stage, sex, and age; Table 2).

Table 1.

Clinicopathologic Features Stratified by BMI Category in Patients With Stage II or III Colon Carcinomas From Randomized Trials of FU-Based Adjuvant Chemotherapy

Variable	Total(N = 2,693)		Underweight(n = 142; 5.3%)		Normal(n = 879; 32.6%)		Overweight(n = 1,042; 38.7%)		Obese(n = 630; 23.4%)		Obese v Normal P	Overall P
Variable	No.	%	No.	%	No.	%	No.	%	No.	%	Obese v Normal P	Overall P
Stage											.2428^*	.4651^†
II	714	26.5	40	28.2	226	25.7	269	25.8	179	28.4
III	1,979	73.5	102	71.8	653	74.3	773	74.2	451	71.6
Site^‡											.0117^*	.0492^*
Distal	1,449	54.4	83	59.3	444	51.2	560	54.5	362	57.7
Proximal	1,214	45.6	57	40.7	424	48.8	468	45.5	265	42.3
Sex											.1146^*	< .001^†
Female	1,240	46	113	79.6	445	50.6	389	37.3	293	46.5
Male	1,453	54	29	20.4	434	49.4	653	62.7	337	53.5
Grade^§											.0418^*	.0048^†
1 to 2 (low)	1,768	77.8	70	68.6	550	76.4	697	77.9	451	81.1
3 to 4 (high)	505	22.2	32	31.4	170	23.6	198	22.1	105	18.9
PS^§											.6412^*	.5249^*
0	2,030	81.8	103	83.7	652	81.3	802	83.4	473	79.5
1	438	17.6	20	16.3	145	18.1	154	16	119	20
2	14	0.6	0	0	5	.6	6	.6	3	.5
Lymph nodes^§											.3143^*	.7966^*
Negative	714	26.6	40	28.2	226	25.8	269	25.9	179	28.4
1-3 positive	1,293	48.1	69	48.6	432	49.3	506	48.7	286	45.4
> 3 positive	681	25.3	33	23.2	219	25	264	25.4	165	26.2
T stage^§											.4030^*	.7150^†
T1-2	299	11.1	8	5.7	103	11.7	123	11.8	65	10.4
T3-4	2,383	88.9	132	94.3	774	88.3	915	88.2	562	89.6
Age, years											.0206^¶	< .001^‖
Mean	59.4		56.1		59.5		60.4		58.4
SD	11.20		12.64		11.74		10.68		10.69
Median	61.0		58.0		61.0		62.0		59.5
Range	21.0-86.2		25.0-76.0		24.0-86.2		21.0-85.0		22.0-81.0
MMR status											< .001^*	< .001^†
pMMR	2,266	84.1	111	78.2	726	82.6	864	82.9	565	89.7
dMMR	427	15.9	31	21.8	153	17.4	178	17.1	65	10.3

Abbreviations: BMI, body mass index; dMMR, deficient mismatch repair; FU, fluorouracil; MMR, mismatch repair; pMMR, proficient MMR; PS, performance status; SD, standard deviation.

^{χ-square test.}

^{Cochran-Armitage trend test.}

^{Nonsignificant trend test}P value = .1069.

^{Missing cases.}

^{Wilcoxon rank sum test.}

^{Kruskal-Wallis exact test.}

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Fig 1.

Percentage of resected colon carcinomas (n = 2,693) showing deficient DNA mismatch repair (dMMR; n = 427) in patients treated in randomized trials of fluorouracil-based adjuvant chemotherapy. Data are shown for (A) percentage of dMMR tumors in normal-weight (153 of 879; 17%) and obese (65 of 630; 10%) patients and (B) stratified by sex within these body mass index categories.

Table 2.

Effect of Obesity on DNA MMR Status in Stage II and III Colon Carcinomas After Adjusting for Covariates (n = 1,495)

Variable	OR	95% CI	P
Obese v normal weight	0.57	0.41 to 0.79	< .001
Proximal v distal	4.01	2.87 to 5.60	< .001
Stage III v stage II	0.39	0.28 to 0.55	< .001
Age (1-year increase)	0.98	0.971 to 0.997	.0195
Male v female	0.75	0.55 to 1.02	.0703

Abbreviations: MMR, mismatch repair; OR, odds ratio.

When analyzed by patient sex, rates of dMMR tumors were lower in obese versus normal-weight men (8% v 17%; P < .001) and women (13% v 18; P = .0817; Fig 1B). Furthermore, obese men were significantly less likely to have dMMR tumors compared with obese women (8% v 13%; P = .0413; Fig 1B).

Association of BMI and MMR Status With Recurrence and Prognosis

Among obese versus normal-weight patients, the 5-year recurrence rates were 32% versus 25.3%, respectively (P = .0034). Time-to-recurrence (TTR) was also shorter in obese versus normal-weight patients (hazard ratio [HR], 1.34; 95% CI, 1.10 to 1.63; P = .0034). Obese patients had significantly worse DFS (HR, 1.35; 95% CI, 1.13 to 1.62; P = .0011) and OS (HR, 1.32; 95% CI, 1.10 to 1.58; P = .0025) rates compared with normal-weight patients (Fig 2; Appendix Table A1, online only). The adverse prognostic impact of obesity was similar in men and in women (DFS: P_interaction = .9377) but was stronger in proximal versus distal tumors (DFS: P_interaction = .0483) compared with normal-weight patients. Specifically, obese patients (v normal-weight patients) with proximal cancers had significantly worse DFS (HR, 1.63; 95% CI, 1.25 to 2.14; P < .001), but an adverse impact was not evident in distal tumors (HR, 1.12; 95% CI, 0.87 to 1.44; P = .3860). Similar results were found within the obese subgroup in which proximal (v distal) tumors had worse outcome for DFS (HR, 1.31; 95% CI, 1.00 to 1.71; P = .0458) and OS (HR, 1.33; 95% CI, 1.02 to 1.74; P = .0334).

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Fig 2.

Prognostic impact of obesity versus normal weight status on (A) overall survival and (B) disease-free survival rates in patients with stage II and III colon carcinoma who participated in fluorouracil-based adjuvant chemotherapy trials. HR, hazard ratio.

Survival rates among overweight and underweight patients did not differ significantly from those of normal-weight patients. Among the underweight, there was a trend toward worse DFS and OS that did not reach statistical significance, possibly because of the limited sample size (n = 142). Tumor stage (III v II) was associated with significantly worse DFS and OS; male sex and older age were associated with significantly worse OS (Appendix Table A1). Patients with dMMR tumors showed significantly better DFS (HR, 0.59; 95% CI, 0.47 to 0.74; P < .001) and OS (HR, 0.63; 95% CI, 0.51 to 0.78; P < .001) rates compared with patients with pMMR tumors (Appendix Table A1). The favorable prognostic impact of dMMR seen in the overall study population was maintained in obese and normal-weight subgroups (P_interaction = .6560; Fig 3).

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Fig 3.

Prognostic impact of deficient mismatch repair (dMMR) versus proficient MMR (pMMR) status for overall survival in (A) normal-weight and (B) obese patients with stage II and III colon cancers. HR, hazard ratio.

In a multivariable analysis, obesity was an independent prognostic factor for worse DFS (HR, 1.37; 95% CI, 1.14 to 1.64; P = .0010), OS (HR, 1.34; 95% CI, 1.12 to 1.61; P = .0017), and TTR (HR, 1.35; 95% CI, 1.11 to 1.64; P = .0032), even after adjusting for stage, tumor site, sex, age, and MMR status (Table 3). When stratified by tumor site, the adverse prognostic impact of obesity (v normal weight) was more evident in proximal versus distal tumors, yet the association weakened after adjustment for covariates, including MMR (DFS: P_interaction= .0746). We also found that dMMR status was independently associated with significantly better DFS and OS rates compared with pMMR status (Table 3). No interdependence between obesity and MMR status was found in the multivariable model (DFS: P_interaction= .4576; OS: P_interaction= .8147).

Table 3.

Multivariable Survival Analysis in Patients With Stage II and III Colon Carcinoma

Variable	DFS HR	95% CI	P^*	OS HR	95% CI	P^*
Obese v normal weight	1.37	1.14 to 1.64	.0010	1.34	1.12 to 1.61	.0017
Stage III v II	2.37	1.82 to 3.07	< .001	2.10	1.64 to 2.69	< .001
Proximal v distal	1.18	0.98 to 1.42	.0894	1.20	1.00 to 1.45	.0568
Men v women	1.07	0.89 to 1.28	.4826	1.21	1.01 to 1.45	.0423
Age (increase of 1 year)	1.01	1.00 to 1.02	.0902	1.02	1.02 to 1.03	< .001
dMMR v pMMR	0.62	0.45 to 0.86	.0023	0.67	0.49 to 0.91	.0082

Abbreviations: DFS, disease-free survival; dMMR, deficient mismatch repair; HR, hazard ratio; OS, overall survival; pMMR, proficient MMR.

^{Likelihood ratio}P value from a Cox regression model after stratifying by study.

Within our study population, a predictive analysis for obesity and the effect of FU-based therapy was not appropriate, given that relatively few patients received surgery alone. In a prior study²⁶ that used participants in NCCTG and Southwest Oncology Group (SWOG) adjuvant studies, we failed to find a significant relationship between BMI category and treatment efficacy for FU in multivariable models.

Patient Characteristics by MMR Status and BMI Category

Table 1.

Clinicopathologic Features Stratified by BMI Category in Patients With Stage II or III Colon Carcinomas From Randomized Trials of FU-Based Adjuvant Chemotherapy

Variable	Total(N = 2,693)		Underweight(n = 142; 5.3%)		Normal(n = 879; 32.6%)		Overweight(n = 1,042; 38.7%)		Obese(n = 630; 23.4%)		Obese v Normal P	Overall P
Variable	No.	%	No.	%	No.	%	No.	%	No.	%	Obese v Normal P	Overall P
Stage											.2428^*	.4651^†
II	714	26.5	40	28.2	226	25.7	269	25.8	179	28.4
III	1,979	73.5	102	71.8	653	74.3	773	74.2	451	71.6
Site^‡											.0117^*	.0492^*
Distal	1,449	54.4	83	59.3	444	51.2	560	54.5	362	57.7
Proximal	1,214	45.6	57	40.7	424	48.8	468	45.5	265	42.3
Sex											.1146^*	< .001^†
Female	1,240	46	113	79.6	445	50.6	389	37.3	293	46.5
Male	1,453	54	29	20.4	434	49.4	653	62.7	337	53.5
Grade^§											.0418^*	.0048^†
1 to 2 (low)	1,768	77.8	70	68.6	550	76.4	697	77.9	451	81.1
3 to 4 (high)	505	22.2	32	31.4	170	23.6	198	22.1	105	18.9
PS^§											.6412^*	.5249^*
0	2,030	81.8	103	83.7	652	81.3	802	83.4	473	79.5
1	438	17.6	20	16.3	145	18.1	154	16	119	20
2	14	0.6	0	0	5	.6	6	.6	3	.5
Lymph nodes^§											.3143^*	.7966^*
Negative	714	26.6	40	28.2	226	25.8	269	25.9	179	28.4
1-3 positive	1,293	48.1	69	48.6	432	49.3	506	48.7	286	45.4
> 3 positive	681	25.3	33	23.2	219	25	264	25.4	165	26.2
T stage^§											.4030^*	.7150^†
T1-2	299	11.1	8	5.7	103	11.7	123	11.8	65	10.4
T3-4	2,383	88.9	132	94.3	774	88.3	915	88.2	562	89.6
Age, years											.0206^¶	< .001^‖
Mean	59.4		56.1		59.5		60.4		58.4
SD	11.20		12.64		11.74		10.68		10.69
Median	61.0		58.0		61.0		62.0		59.5
Range	21.0-86.2		25.0-76.0		24.0-86.2		21.0-85.0		22.0-81.0
MMR status											< .001^*	< .001^†
pMMR	2,266	84.1	111	78.2	726	82.6	864	82.9	565	89.7
dMMR	427	15.9	31	21.8	153	17.4	178	17.1	65	10.3

Abbreviations: BMI, body mass index; dMMR, deficient mismatch repair; FU, fluorouracil; MMR, mismatch repair; pMMR, proficient MMR; PS, performance status; SD, standard deviation.

^{χ-square test.}

^{Cochran-Armitage trend test.}

^{Nonsignificant trend test}P value = .1069.

^{Missing cases.}

^{Wilcoxon rank sum test.}

^{Kruskal-Wallis exact test.}

Fig 1.

Table 2.

Effect of Obesity on DNA MMR Status in Stage II and III Colon Carcinomas After Adjusting for Covariates (n = 1,495)

Variable	OR	95% CI	P
Obese v normal weight	0.57	0.41 to 0.79	< .001
Proximal v distal	4.01	2.87 to 5.60	< .001
Stage III v stage II	0.39	0.28 to 0.55	< .001
Age (1-year increase)	0.98	0.971 to 0.997	.0195
Male v female	0.75	0.55 to 1.02	.0703

Abbreviations: MMR, mismatch repair; OR, odds ratio.

Association of BMI and MMR Status With Recurrence and Prognosis

Fig 2.

Fig 3.

Table 3.

Multivariable Survival Analysis in Patients With Stage II and III Colon Carcinoma

Variable	DFS HR	95% CI	P^*	OS HR	95% CI	P^*
Obese v normal weight	1.37	1.14 to 1.64	.0010	1.34	1.12 to 1.61	.0017
Stage III v II	2.37	1.82 to 3.07	< .001	2.10	1.64 to 2.69	< .001
Proximal v distal	1.18	0.98 to 1.42	.0894	1.20	1.00 to 1.45	.0568
Men v women	1.07	0.89 to 1.28	.4826	1.21	1.01 to 1.45	.0423
Age (increase of 1 year)	1.01	1.00 to 1.02	.0902	1.02	1.02 to 1.03	< .001
dMMR v pMMR	0.62	0.45 to 0.86	.0023	0.67	0.49 to 0.91	.0082

Abbreviations: DFS, disease-free survival; dMMR, deficient mismatch repair; HR, hazard ratio; OS, overall survival; pMMR, proficient MMR.

^{Likelihood ratio}P value from a Cox regression model after stratifying by study.

DISCUSSION

We studied the association of BMI with the status of the DNA MMR system in patients with resected colon cancers who participated in adjuvant chemotherapy trials. Overall, obesity was associated with a significantly lower rate of dMMR compared with all other BMI categories. Specifically, obese patients had a 43% lower odds of having a dMMR tumor compared with normal-weight patients after adjusting for covariates associated with MMR status. Theses data indicate that obesity-associated colon cancers are predominantly of the pMMR molecular subtype that shows chromosomal instability⁴⁸ and exhibits more aggressive behavior compared with dMMR tumors.⁶,9–13 In this regard, obesity and pMMR were each independently associated with adverse clinical outcome. Our data expand the molecular phenotype of obesity-associated colon cancers to include increased rates of pMMR. The relationship between prediagnosis BMI, MSI status, and CRC risk was examined in a case-control study in which a high BMI (self-reported) was associated with an increased risk of developing CRCs showing MSS but not MSI-H.⁴⁹ Together with our study findings, these data suggest that obesity may influence the molecular pathogenesis of colon cancer and reduce the favorable prognostic dMMR subtype.

A majority of dMMR colon cancers in our series are expected to be sporadic with inactivation of MLH1 in association with a dense pattern of DNA methylation near gene promoter regions termed the CpG island methylator phenotype (CIMP-high).¹ In a study examining lifestyle factors and CIMP status, obesity was associated with a two-fold increased risk of having a CIMP-low tumor but did not influence CIMP-high tumors.¹⁸ Since CIMP is a pathway that inactivates MLH1,³,50 this finding is consistent with our study finding of a lower rate of dMMR in colon cancers observed among obese patients. A mechanistic link may exist between obesity and DNA methylation. Sirtuin 1 (SIRT1), a histone deacetylase, is important in epigenetic gene silencing and was shown to be overexpressed in colon cancers in association with CIMP-high status and dMMR.⁵¹ However, SIRT1 levels decrease in obesity with the potential to reactivate silenced genes that could influence MMR status in obese patients. SIRT1 increases metabolic efficiency and may provide a link between obesity, energy balance, and cancer.⁵²

Overall, we found a higher frequency of dMMR in women compared with men, especially women over the age of 50 years when this age cutoff was used as a surrogate for menopausal status. These results are consistent with data demonstrating that female sex is an independent predictor of dMMR due to MLH1 methylation with advancing age.¹ Furthermore, data suggest that estrogen production may protect against dMMR, whereas a lack of endogenous estrogen in postmenopausal women may increase the risk of dMMR tumors.¹⁸,49 Interestingly, we found that obese men had significantly lower rates of dMMR compared with normal-weight men, but this effect did not reach statistical significance in women. Furthermore, obese men had significantly lower rates of dMMR compared with obese women. Obesity is associated with an increased production of estrogens in both sexes that is due to extragonadal aromatization of androgens and decreased plasma levels of sex hormone–binding globulin that binds estradiol.²⁹,53,54 Although the mechanism underlying the lower rate of dMMR tumors in obese men is unknown and likely to be multifactorial, contributing factors include the lower overall rate of dMMR in men and increased levels of estrogen that could potentially suppress dMMR.

Obese patients with colon cancer had significantly higher recurrence rates, shorter TTR, and worse DFS and OS rates compared with normal-weight patients, even after adjusting for tumor site, stage, age, sex, and MMR status. The effect of obesity on patient survival was more evident in proximal compared with distal colon cancers, suggesting that obesity-associated biologic effects may influence tumor behavior in a site-dependent manner. The prognostic impact of obesity was similar in men and women. An adverse impact for obesity and colon cancer prognosis has been previously reported by our group²⁶ and others.²⁸,55 Patients with dMMR colon cancers had a statistically significant improvement in DFS and OS compared with pMMR tumors, which did not differ significantly across BMI categories. Therefore, the favorable prognostic impact of dMMR was maintained despite the presence of obesity. Although obesity is associated with an increased risk and worsened prognosis for colorectal and other types of cancer, the mechanisms underlying the obesity-cancer progression link are poorly understood. In addition to insulin resistance and hyperinsulinemia, obesity is associated with alterations in the insulin-like growth factor-1 axis, adipocyte production of adipokines including leptin,⁵⁶,57 and proinflammatory mediators that may be important contributors to tumor development and progression.⁵⁸,59

Strengths of our study include the large number of dMMR colon cancers evaluated and the meticulous collection of long-term follow-up data within the context of clinical trials. In contrast to other studies of BMI and MMR status in which BMI was calculated from patient-reported data and recall, the recording of height and weight was performed in our study by trained medical personnel at study enrollment. The frequency of dMMR reported here is consistent with multiple clinic and population-based studies.¹,13 Since obesity is associated with comorbid illness, the strict inclusion criteria of the clinical trials requiring normal organ function and favorable performance status serve to minimize the effect of comorbidities on clinical outcome. Limitations of this study include its retrospective design and the fact that our study cohort represents a subset of the overall study populations from individual adjuvant therapy trials based on tissue availability. Furthermore, we did not have information on menopausal status or hormone replacement therapy for our study cohort.

In summary, obesity is independently associated with the molecular subtype of pMMR colon cancer that shows significantly worse survival rates compared with dMMR tumors. In fact, both obesity and MMR status were independent prognostic variables in patients with stage II or III colon cancer. Importantly, the favorable prognosis of dMMR tumors was maintained in obese patients. Together, these data indicate that colon cancers from obese patients are less likely to develop via the dMMR pathway and have a worse prognosis compared with those in normal-weight patients that is independent of other tumor variables.

Frank A. Sinicrope, Nathan R. Foster, Harry H. Yoon, Thomas C. Smyrk, Daniel A. Nikcevich, and Daniel J. Sargent, North Central Cancer Treatment Group, Mayo Clinic, Rochester; Daniel A. Nikcevich, Duluth Community Clinical Oncology Program, Essentia Health, Duluth, MN; George P. Kim, Mayo Clinic, Jacksonville; Carmen J. Allegra, University of Florida, Gainesville, FL; Greg Yothers, University of Pittsburgh Graduate School of Public Health; and Carmen J. Allegra and Greg Yothers, National Surgical Adjuvant Breast and Bowel Project, Pittsburgh, PA.

Corresponding author: Frank A. Sinicrope, MD, FACP, Mayo Clinic and Mayo Cancer Center, 200 1st St SW, Rochester, MN 55905; e-mail: ude.oyam@knarf.eporciniS.

Received 2011 Sep 13; Accepted 2011 Nov 2.

Abstract

Purpose

Although the importance of obesity in colon cancer risk and outcome is recognized, the association of body mass index (BMI) with DNA mismatch repair (MMR) status is unknown.

Patients and Methods

Results

Conclusion

Abstract

Abbreviations: BMI, body mass index; dMMR, deficient mismatch repair; FU, fluorouracil; MMR, mismatch repair; pMMR, proficient MMR; PS, performance status; SD, standard deviation.

Abbreviations: MMR, mismatch repair; OR, odds ratio.

Abbreviations: DFS, disease-free survival; dMMR, deficient mismatch repair; HR, hazard ratio; OS, overall survival; pMMR, proficient MMR.

NOTE. Boldface indicates statistically significant P values.

Abbreviations: BMI, body mass index; DFS, disease-free survival; dMMR, deficient mismatch repair; MMR, mismatch repair; OS, overall survival; pMMR, proficient mismatch repair.

Footnotes

Supported, in part, by Grant No. K05CA-142885 (Senior Scientist Award to F.A.S.) from the National Cancer Institute, National Institutes of Health.

Authors' disclosures of potential conflicts of interest and author contributions are found at the end of this article.

Clinical trial information can be found for the following: {"type":"clinical-trial","attrs":{"text":"NCT00004931","term_id":"NCT00004931"}}NCT00004931.

Footnotes

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