Using immunohistochemistry to classify the molecular subtypes of Paget's disease of the breast

PURPOSE: To classify the molecular subtypes of Paget's disease of the breast, and then compare them with general breast cancer to get deeper understanding of this disease and offer better management of associate patients in clinical decisions. METHODS: We used immunohistochemistry to examine 42 cases of this disease by antibodies against estrogen and progesterone receptors, Ki‐67, as well as human epidermal growth factor receptor 2 (HER‐2). Due to damage and loss of specimens, etc., we obtained 36 pathological specimens from the 42 patients. For 30 of 36 pathological specimens (83.3%), we obtained a complete molecular subtype. Cause the other 6 pathological specimens have missing immunohistochemistry items. For patients with bilateral breast cancer, only information on the side with PDB is listed. For patients with recurrence, only information on the first onset was included. We finally compared and studied the molecular subtype of 26 samples. We calculated the relative frequencies of molecular subtypes including luminal A, luminal B, HER‐2‐enriched, and basal‐like and compared them between PDB and general breast carcinomas in other studies. RESULTS: The luminal A and B subtype were found, respectively, in 3 (11.5%) and 6 (23.1%) of all patients, and 15 cases of HER‐2‐enriched subtype was detected (57.7%). In addition, 2 (7.7%) showed a basal‐like subtype. CONCLUSION: The molecular subtypes of common breast cancer and PDB‐associated breast cancer differ. Luminal subtypes are the most common in the former, while within our samples HER‐2 positive subtype was the highest in PDB‐associated breast carcinoma. With further understanding of this disease, rational therapies will be applied in different patients and cures for PDB and PDB‐associated carcinoma will be achieved.