Intracystic papillary carcinoma of the breast: a diagnostic challenge with major clinical impact.

BACKGROUND: Intracystic papillary carcinoma (IPC) is a ductal carcinoma of papillary variety that develops in a cystic space surrounded by a fibrous capsule. It is a rare clinicopathological entity, the in situ or invasive character of which is difficult to establish, particularly on biopsy. The treatment is surgical and breast conservation depends on the tumor size. Lymph node exploration is still debated. The diagnosis of IPC is a challenge for the pathologist: the negativity of the basement membrane markers and of myoepithelial cells carries a risk of over-diagnosis on biopsy that can lead to over-treatment. CASE REPORT: To illustrate this risk, we report the case of a breast mass of 8 cm; its biopsy evoked invasive papillary carcinoma (no hormone receptors and overexpression of Human Epidermal Receptor-2 (HER-2) and for which neoadjuvant chemotherapy associated with trastuzumab was firstly proposed. RESULTS: The analysis of all anatomical radio-clinical data in a multidisciplinary context, however, allowed suspecting IPC, thus leading to first-line surgery (mastectomy with negative sentinel lymph nodes). With this diagnosis being confirmed on surgical specimen, no systemic treatment was then necessary. After 48 months, the patient is in complete remission.