Background: Triple-negative breast cancers (TNBCs) and basal-like breast cancers (BLBCs) are known as poor outcome subtypes with a lack of targeted therapy. Previous studies have shown conflicting results regarding the difference of prognostic significance between TNBCs and BLBCs. In this study, we aimed to characterize the prognostic features of TNBCs, in view of BLBCs and quintuple-negative breast cancers (QNBC/5NPs). Methods: Using tissue microarray-based immunohistochemical analysis, we categorized 951 primary breast cancers into four or five subtypes according to the expression of ER, PR, HER2, and basal markers (CK5/6, EGFR). Results: The results of this study showed that both TNBCs and BLBCs were associated with high histological and/or nuclear grades. When the TNBCs are divided into two subtypes by the presence of basal markers, the clinicopathologic characteristics of TNBCs were mainly maintained in the BLBCs. The 5-subgrouping was the better prediction model for both disease free and overall survival in breast cancers than the 4-subgrouping. After multivariate analysis of TNBCs, the BLBCs did not have a worse prognosis than the QNBC/5NPs. Interestingly, the patients with BLBCs showed significant adjuvant chemotherapy benefit. In addition, QNBC/5NPs comprised about 6~8% of breast cancers in publicly available breast cancer datasets Conclusion: The QNBC/5NP subtype is a worse prognostic subgroup of TNBCs, especially in higher stage and this result may be related to adjuvant chemotherapy benefit of BLBCs, calling for caution in the identification of subgroups of patients for therapeutic classification.

The p16INK4a gene methylation has been reported to be a major tumorigenic mechanism. We evaluated the methylation status of the p16INK4a genes in 231 invasive breast cancer and 90 intraductal carcinoma specimens using a methylation-specific polymerase chain reaction and p16 protein expression using immunohistochemistry. The quantity of cell-free methylated p16INK4a DNA in the plasma samples of 200 patients with invasive breast cancer was also examined using a fluorescence-based real-time polymerase chain reaction assay. The frequencies of p16INK4a methylation in invasive and intraductal tumors were 52.8% (122/231) and 57.8% (52/90), respectively. The p16 protein was overexpressed in 145 of the 231 invasive carcinomas (62.8%) and 63 of the 90 intraductal carcinomas (70%). High p16 expression in invasive carcinomas correlated significantly with a high histologic grade, a negative estrogen receptor and progesterone receptor status, p53 immunoreactivity and high Ki-67 expression with immunohistochemistry. In addition, the methylation index of p16INK4a was significantly higher in the cancer patients than the normal controls (p<0.001). High p16 immunoreactivity correlated with a loss of differentiation in breast carcinomas and high frequency of p16INK4a promoter methylation in both invasive and intraductal carcinomas, suggesting it may be involved in the pathogenesis of breast cancer.

Pathologic complete response (pCR) after neoadjuvant chemotherapy (NAC) has been associated with favorable clinical outcome in breast cancer patients. However, the possibility that the prognostic significance of pCR differs among various definitions has not been established. We retrospectively evaluated the pathologic response after NAC in 353 breast cancer patients and compared the prognoses after applying the following different definitions of pCR: ypT0/is, ypT0, ypT0/is ypN0, and ypT0 ypN0. pCR was significantly associated with improved distant disease-free survival (DDFS) regardless of the definition (ypT0/is, p = .002; ypT0, p = .008; ypT0/is ypN0, p < .001; ypT0 ypN0, p = .003). Presence of tumor deposits of any size in the lymph nodes (LNs; ypN ≥ 0(i+)) was associated with worse DDFS (ypT0 ypN0 vs ypT0 ypN ≥ 0(i+), p = .036 and ypT0/is ypN0 vs ypT0/is ypN ≥ 0(i+), p = .015), and presence of isolated tumor cells was associated with decreased overall survival (OS; ypT0/is ypN0 vs ypT0/is ypN0(i+), p = .013). Residual ductal carcinoma in situ regardless of LN status showed no significant difference in DDFS or OS (DDFS: ypT0 vs ypTis, p = .373 and ypT0 ypN0 vs ypTis ypN0, p = .462; OS: ypT0 vs ypTis, p = .441 and ypT0 ypN0 vs ypTis ypN0, p = .758). In subsequent analysis using ypT0/is ypN0, pCR was associated with improved DDFS and OS in triple-negative tumors (p < .001 and p = .003, respectively). Based on our study results, the prognosis and rate of pCR differ according to the definition of pCR and ypT0/is ypN0 might be considered a more preferable definition of pCR.