Garrity, Megan M

10022 Background: Patients with colon cancers displaying high frequency microsatellite instability (MSI-H) are reported to have a favorable prognosis compared to microsatellite stable (MSS) tumors. However, prognostic factors underlying this observation are poorly understood. We studied apoptotic and proliferative indices and their relationship to MSI status, clinicopathological features, and patient survival rates. Methods: Archival Dukes’ stage B2 (n=83) and C (n=246) primary colon adenocarcinomas from patients enrolled in five 5-fluorouracil-based adjuvant therapy trials were analyzed for MSI using a PCR-based assay (MSI-H: ≥30% of loci with instability), and expression of hMLH1, hMSH2 and p53 proteins by immunostaining. Apoptosis was analyzed by the TUNEL assay and the proliferative index (PI: S phase + G2M) and DNA ploidy by flow cytometry. Correlations between markers and associations with overall survival (OS) censored at 8 yrs were sought. Results: MSI-H (n=58.18%) tumors were more likely proximal, diploid, high grade, p53 negative (vs. MSS/MSI-L; all p<0.0001), and from women (p=0.002). Of 58 MSH-H cases tested, 54 showed loss of hMLH1 (n=50) or hMSH2 (n=4) proteins. Median proliferative index (PI) [12.6 vs. 17.4; p=0.0002] was reduced in MSI-H versus MSS/MSI-L tumors. Lower PI was associated with diploidy (p<0.0001) and negative p53 expression (p=0.003). Apoptotic indices (AIs) were increased in MSI-H cancers (vs. MSS/MSI-L, p=0.082), as was the AI/PI ratio (p=0.0065). Interestingly, AI (p=0.02) and AI/PI (p<0.0001) were significantly increased in diploid versus nondiploid tumors, and after removal of MSI-H cases, relationships held for PI and AI/PI with ploidy. Better OS was related to MSI-H (p=0.032), loss of hMLH1 or hMSH2 (p=0.024), diploidy (p=0.0015), and lower PI (p=0.078), but not AI, AI/PI, nor p53 (adjusting for stage, grade, treatment and stratifying by study). Conclusions: MSI-H tumors are characterized by reduced proliferative indices and a higher ratio of apoptosis to proliferation, reflecting slower tumor growth rates compared to MSS/MSI-L tumors. These features may contribute to their better survival. Lower PI and increased AI/PI are also features of diploid MSS cancers. [Table: see text]

Purpose Molecular studies of colon cancer have provided insights into pathogenesis, yet it is unclear how important these markers are in predicting prognosis. This study investigated the prognostic significance of TUNEL, bcl-2, p53, proliferation marker Ki-67 and DNA mismatch repair (MMR) status in patients with Dukes' stage B2 and C colorectal adenocarcinomas. Patients and Methods Tumor tissue from 366 patients (75% Dukes' C, 25% Dukes' B2) from four randomized North Central Cancer Treatment Group phase III surgical adjuvant trials were used. Eighty-one percent of patients received adjuvant treatment, which was primarily fluorouracil (FU) based (90%). Tumor location was predominantly (87%) the colon. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL), Ki-67, p53, bcl-2, and MMR were assayed using immunohistochemistry. Stage, grade, MMR, Ki-67, and previously determined flow cytometry markers (ploidy and S phase) were explored for associations with each other and with overall survival (OS) and disease-free survival (DFS). Results Univariately, stage B2, low grade, diploid, Ki-67 more than 27%, normal p53, and FU-based adjuvant treatment were significantly associated with improved OS and DFS (P < .05). After adjusting for stage, grade, and ploidy in multivariate analysis, Ki-67 remained significantly related to both OS and DFS (P < .01). Active FU-based adjuvant treatment was significant only for OS in this multivariate model. Neither bcl-2 nor TUNEL were significant. Conclusion This retrospective study indicates that Ki-67 and ploidy may have stronger prognostic impact on OS and DFS than other parameters investigated after adjusting for stage and tumor grade. Prospective studies to elucidate the mechanism and prognostic significance of these findings are necessary.