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

Background: The relationship between the pathologic response patterns after neoadjuvant chemotherapy (NAC) and specific subtypes of breast cancer is unclear.

Methods: 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.

Results: 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.

Conclusion: The molecular subtypes of breast cancer have characteristic pathologic patterns of response to NAC.