Intracystic papillary carcinoma of the breast: An in situ or invasive tumor? Results of immunohistochemical analysis and clinical follow-up.

Intracystic papillary carcinoma (IPC) is regarded as an intraductal neoplasm, but recent evidence suggests that it could be invasive, as it often lacks myoepithelial lining. We evaluated myoepithelial cells and collagen IV, a basement membrane component, in 40 IPCs from 39 (35 female and 4 male) patients and assessed their clinical management and follow-up. The mean patient age at diagnosis was 68 years, and the mean tumor size was 1.8 cm. Thirteen cases were pure IPC, 8 cases were IPC with or without microinvasion, and 19 cases were IPC with invasive carcinoma (IPC+IC), including 1 mucinous and 1 cribriform carcinoma. Ductal carcinoma in situ associated more often with IPC+IC (84.2%) than with pure IPC (61.5%) or IPC with or without microinvasion (62.5%). Myoepithelial cells were completely absent in 33 of 40 (82.5%) IPCs, and only focal in the remaining 7 of 40 cases (17.5%). Collagen IV lining was discontinuous in most cases (89%). All tumors were estrogen receptor positive and HER2 negative; most were progesterone receptor positive (93%). Eleven patients underwent mastectomy and 28 lumpectomy; 3 of 27 (11%) patients had lymph node involvement. Fourteen of all patients treated with breast conservation received radiation, 10 hormonal treatment, and none chemotherapy. Four patients treated conservatively (3 with pure IPC and 1 with IPC+IC) recurred locally, including one who later developed bone metastasis. We conclude that IPC constitutes a spectrum of intraductal and IC, with predominance of the latter. IPC rarely involves lymph nodes and carries very good prognosis, but can recur locally. This type of tumor is strongly estrogen receptor positive and hormonal therapy should be pursued for its management, whereas the benefit of radiation after lumpectomy remains unclear.