Correlations Between Molecular Subtypes and Pathologic Response Patterns of Breast Cancers After Neoadjuvant Chemotherapy

The relationship between the pathologic response patterns after neoadjuvant chemotherapy (NAC) and specific subtypes of breast cancer is unclear. This study retrospectively analyzed 351 tumors from 348 women with breast cancer who received anthracycline and taxane-based NAC and subsequent surgery. Various histopathologic factors were assessed in the pretreatment biopsy and surgery specimens based on molecular subtypes defined by immunohistochemistry. The tumors without a pathologic complete response in each subtype retained their morphologic features after NAC. Lymphocytic infiltration was higher in the hormone receptor-negative (HR-) tumors than in the HR+ tumors. The HR- tumors showed more necrosis and histiocytic infiltration in the tumor bed than the HR+ tumors. The overall (including in situ carcinoma) and invasive pathologic cancer sizes were similar for the triple-negative tumors only. Although all the subtypes showed significantly reduced tumor size after NAC, the difference between the pre-NAC magnetic resonance imaging (MRI) tumor size and the overall pathologic cancer size was significantly smaller for the HR+/human epidermal growth factor receptor 2-negative (HER2-) subgroup than for the triple-negative subgroup. The triple-negative tumors showed the highest correlation between post-NAC tumor size measured by MRI and overall or invasive pathologic tumor size. The molecular subtypes of breast cancer have characteristic pathologic patterns of response to NAC.