Mucinous Carcinoma with Extensive Signet Ring Cell Differentiation: A Case Report

Area of Science:

• Oncology
• Pathology

Background:

• Breast cancers can exhibit mucinous features, including mucinous carcinoma (extracellular mucin) and signet ring cell carcinoma (intracellular mucin).
• Differentiating primary breast tumors from metastatic disease is crucial for accurate diagnosis and treatment.

Purpose of the Study:

• To describe a unique case of breast cancer presenting with both extracellular mucin and extensive signet ring cell differentiation.
• To highlight key pathological and immunohistochemical features that distinguish this presentation from conventional mucinous carcinoma and aid in identifying the breast as the primary origin.

Main Methods:

• Histopathological examination of tumor morphology, including assessment of mucin distribution (intracellular vs. extracellular).
• Evaluation of nuclear grade, mitotic index, and immunohistochemical markers such as estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor-2 (HER2), E-cadherin, mammaglobin, and gross cystic disease fluid protein-15 (GCDFP-15).

Main Results:

• The case exhibited abundant intracellular mucin (signet ring cells) and extracellular mucin.
• Distinct features included high-grade nuclear pleomorphism, high mitotic index, ER negativity, PR negativity, HER2 positivity, and E-cadherin positivity, indicative of a ductal type.
• The presence of ductal carcinoma in situ, mammaglobin, and GCDFP-15 positivity supported a breast origin.

Conclusions:

• This case represents a rare variant of breast cancer combining features of mucinous carcinoma and signet ring cell carcinoma.
• Specific pathological and immunohistochemical markers are essential for differentiating this breast tumor from metastatic signet ring cell carcinoma of gastrointestinal origin.