Objective  To investigate the differences in shrinkage mode of the primary tumor in patients with different molecular subtypes of breast cancer after neoadjuvant chemotherapy (NAC).

  Methods  One hundred and eight patients with breast invasive ductal carcinoma received NAC from July 2008 to October 2017 at Shandong Cancer Hospital Affiliated to Shandong University. After surgery, the surgical specimens were used to generate large continuous pathological sections. Using electron microscopy, the residual tumor range was delineated, residual tumor was reconstructed in three dimensions, and pathological regression pattern of the primary tumor after NAC was evaluated.

  Result  Luminal A type accounted for 47.4% (9/19) and 52.6% (10/19) of patients with concentric shrinkage mode (CSM) and non-CSM (NCSM) after NAC, respectively. Luminal B human epidermal growth factor receptor 2 (HER2)+ type and HER2+ type accounted for 53.6% (15/28) and 72.7% (16/22) and 46.4% (13/28) and 27.3% (6/22) of patients, respectively. HER2+type accounted for 84.6% (11/13) and 15.4% (2/13) of patients, respectively, and triple-negative breast cancer accounted for 80.8% (21/26) and 19.2% (5/26) of patients, respectively.

  Conclusions  Luminal B HER2+, HER2+, and basal-like types were more likely to have concentric shrinkage mode. The luminal A and luminal B HER2- type had no significant difference in primary tumor regression patterns. Molecular typing is helpful for predicting the regression mode of primary tumors after NAC in patients with breast cancer, which facifitates the selection of appropriate patients for breast-conserving therapy and redution of the local recurrence rate after NAC.