# Subnipple Cyst Formation Is an Important Diagnostic Clue for Mixed-Type Squamous Cell Carcinomas of the Breast: A Case Report

## TL;DR

A breast tumor with a subnipple cyst and adjacent solid mass may indicate a mixed-type squamous cell carcinoma, which is important for accurate diagnosis.

## Contribution

This case report highlights subnipple cyst formation as a diagnostic clue for mixed-type breast SCCs.

## Key findings

- The tumor had a subnipple cyst connected to a solid mass with features of scirrhous-type IDC and SCC.
- Immunostaining showed HER2 negativity in IDC and equivocality in SCC components, with no HER2 amplification confirmed.
- The patient had a successful outcome with surgery and chemotherapy, emphasizing the importance of early diagnosis.

## Abstract

It is well known that breast squamous cell carcinomas (SCCs) have highly cystic components. It, however, is not yet known whether the location of cystic areas contributes to the diagnosis of breast SCCs. A 62-year-old woman with a right breast mass was referred to our hospital. Mammography showed an oval mass just under the right nipple and distortion of the adjacent mammary gland with pleomorphic calcifications. Ultrasound showed a subnipple large oval cystic lesion with solid parts, microcalcifications, and an adjacent polygonal mass, both with a high depth/width ratio and internal punctuate high echoes. Magnetic resonance imaging (MRI) of the masses clarified the connection between the two masses at their deep borders and showed low signals on T1-weighted images and high and slightly high signals at the cyst and mass parts on T2-weighted images, respectively. Core needle biopsy of the solid mass pathologically showed atypical cells growing in tubular and cord-like fashions with connective tissue proliferation, leading to the diagnosis of scirrhous type invasive ductal carcinoma (IDC). The patient, therefore, underwent mastectomy and sentinel node biopsy, showing pathological node negativity on frozen section. Postoperative pathological study showed that the scirrhous type IDC cells were connected to pleomorphic spindle cells and further tied up to SCC cells with central cystic structures. In addition to estrogen and progesterone receptor negativity, immunostaining showed human epidermal growth factor receptor type 2 (HER2) negativity in the IDC components and equivocality in the SCC components. Thereafter, fluorescence in situ hybridization clarified no amplification of human epidermal growth factor receptor type 2 (HER2) genes in the SCC components. The patient recovered uneventfully, received dose-dense chemotherapy, and is scheduled for long-term follow-up on an outpatient basis. Diagnostic physicians should consider mixed-type breast SCCs when breast tumors have cystic structures just under the nipple and an adjacent solid mass.