Microsatellite instability is correlated with lymph node-positive breast cancer

We analyzed 81 cases of primary breast carcinoma and 7 cases of fibroadenoma for microsatellite instability at eight loci. Twenty-seven cases (33.3%) manifested aberrant microsatellite alleles: 7 (8.6%) at one locus and 20 (24.7%) at two or more loci [tumors with replication error-positive (RER+) phenotype]. No evidence of microsatellite instability was observed in fibroadenomas. We investigated correlations between RER+ phenotype and clinicopathological characteristics of the carcinomas. The RER+ phenotype was statistically associated with large tumor diameter; of 19 RER+ tumors with measured size, 16 were >2 cm, compared to 28 of 58 tumors with no evidence of microsatellite instability or with shifts in allele sizes limited to one locus (P ≤ 0.005, χ² test). Consistently, there was also a strong statistical association between RER+ phenotype and lymph node metastasis; 14 of 19 RER+ tumors with known lymph node status were N+, compared to 15 of 59 tumors with no evidence of microsatellite instability or with allele shifts limited to one locus (P ≤ 0.0002, χ² test). Correlations with age of patients, proliferative activity, histotype (ductal versus lobular), and grade of differentiation were not statistically significant, although the RER+ phenotype was more frequent in lobular and high-grade ductal carcinomas, in carcinomas with high proliferative activity, and in carcinomas from patients ≤ 50 years. Data concerning cancer(s) in first and/or second degree relatives were available for 66 cases, including 33 positive and 33 negative for family history of cancer. No correlations were detected between RER+ phenotype and family history of cancer. In conclusion, our results indicate that in breast cancer, microsatellite instability is associated with clinicopathological parameters that are considered predictors of recurrent disease and aggressive behavior.