Primary Mucinous Cystadenocarcinoma of the Breast: Cytologic Finding and Expression of MUC5 Are Different from Mucinous Carcinoma
A 59-year-old postmenopausal woman presented with an illdefined, hard mass in her left breast for a year. Radiologic evaluations demonstrated a hypo-echoic mass (14 mm) with a speculated margin in ultrasonography and a focal asymmetric density in the upper medial portion by mammography. Fine needle aspiration followed by needle biopsy was performed with the diagnosis of MC and invasive carcinoma with abundant mucin pool formation, respectively. She underwent partial mastectomy with sentinel lymph node biopsy. The sentinel lymph node was free from metastasis. She has been followed for 3 months with chemotherapy for adjuvant treatment and remains disease-free.\nThe aspiration showed a few scattered, variably sized, irregular clusters of columnar cells in the greenish blue mucinous background with necrotic debris. The columnar cells contained abundant mucin vacuoles in cytoplasm which had displaced their nuclei. The nuclear membrane was irregular and sharply angulated and the nuclei revealed a coarse chromatin pattern with prominent nucleoli ().\nOn gross examination, the cut surface showed an irregular, white to tan, solid and firm mass (9×7 mm), with a glistening appearance. Most MCAs in previous reports have demonstrated grossly cystic cut surfaces, except one case of MCA reported from Koenig and Tavassoli in 1998.,- The case in 1998 was small in size (8 mm) and had a grossly solid appearance. The present case was 9 mm in maximal diameter and did not contain a macroscopic cyst. It is assumed that the small size of the MCA meant that it did not produce enough mucin to fill out and dilate cysts and ductal structures. The microscopic findings revealed a few cysts and ductal carcinoma in situ, adjacent to the invasive carcinoma. The cysts were lined by a single layer of tall columnar mucinous cells with focal areas of micropapillary structures, resembling those of the uterine endocervix. The luminal space contained mucin (). The invasive cancer area contained an abundant mucin pool in stroma with floating cell clusters. The floating cells contained mucin vacuoles in cytoplasm displacing atypical nuclei to the periphery.\nSpecial staining and IHC on paraffin embedded tissue were performed. Both intracytoplasmic and extracytoplasmic mucin were stained by periodic acid-Schiff with diastase, alcian blue and mucicarcine, representing the acidic and neutral nature of mucin. The tumor cells were positive for CK7 and negative for CK20 and CDX-2. The IHC for MUC proteins was performed. The cancer cells were positive for MUC5 and MUC1 and negative for MUC2 and MUC6. Mucin of the intracytoplasm and stroma revealed positivity for MUC5 and negativity for the other MUC proteins (MUC1, MUC2, and MUC6). The hormone receptors, ER and PR, were negative. The c-erbB2 was 2-positive (), but silver in situ hybridization demonstrated no amplification of the HER-2 gene.