Abstract: This report details the case of a 56-year-old postmenopausal woman diagnosed with metaplastic carcinoma of the breast (squamous cell carcinoma) that subsequently metastasized to the chest wall, sternum, and lungs. The report outlines the diagnostic workup, surgical procedures, adjuvant therapy regimens, and successful treatment response.

Introduction: Metaplastic carcinoma of the breast is a rare and aggressive form of breast cancer. It typically presents as a firm, non-tender mass and lacks the usual hormone receptor expression seen in other breast cancers. This case report highlights the diagnostic approach, treatment course, and successful response to a multimodal treatment strategy for a patient with metaplastic carcinoma of the breast and subsequent distant metastasis.

Case Presentation:

• A 56-year-old postmenopausal woman presented with a painless lump in her right breast.

• Physical examination revealed a 2 x 1.5 cm firm, movable, and irregular mass.

• Mammography and ultrasound identified an abnormal density and calcification in the right breast with suspicious lymph nodes.

• Ultrasound-guided core needle biopsy confirmed low-grade ductal carcinoma in situ with suspicious microinvasion.

• Systemic workup ruled out distant metastases of other primary tumors.

• The patient underwent a modified radical mastectomy with right axillary lymph node dissection.

• Final pathology revealed a 2.5 cm squamous cell carcinoma (histological grade III) with positive lymph node involvement (3 out of 21).

• Immunohistochemistry showed negative estrogen receptor (ER), progesterone receptor (PR), and HER2 receptor status.

• Post-surgery, the patient received adjuvant chemotherapy with epirubicin, cyclophosphamide, followed by docetaxel.

• Adjuvant radiotherapy was delivered to the chest wall and supraclavicular area.

Disease Course and Management of Recurrence:

• Two years later (2017), a PET/CT scan revealed a suspicious mass on the chest wall and sternum, suggestive of metastasis.

• The patient underwent surgical resection of the chest wall lesion.

• Pathology confirmed moderately differentiated squamous cell carcinoma with positive nerve and vascular invasion.

• Further chemotherapy with liposomal paclitaxel and carboplatin was administered followed by single-field electron beam radiation therapy.

• In 2019, a PET/CT scan identified new lesions in the lungs and mediastinal lymph nodes, suggestive of metastatic spread.

• Biopsy confirmed lung metastasis of squamous cell carcinoma originating from the breast cancer.

• The patient received combination chemotherapy with albumin paclitaxel, cisplatin, and immunotherapy with nivolumab.

• After four cycles, a PET/CT scan showed a complete response (CR) with no evidence of lung nodules or mediastinal lymph node enlargement.

• Nivolumab immunotherapy was continued for one year for maintenance.

Discussion: This case demonstrates the aggressive nature of metaplastic carcinoma of the breast with its propensity for distant metastasis. The patient received a multimodality treatment approach, including surgery, chemotherapy, radiation therapy, and immunotherapy, which resulted in a complete response.

Conclusion: This case highlights the importance of a comprehensive diagnostic workup for breast lumps, particularly in postmenopausal women. Multimodality treatment with surgery, chemotherapy, radiation therapy, and potentially immunotherapy may be necessary for patients with metaplastic carcinoma and distant metastasis. Close follow-up is crucial for early detection and management of potential recurrences.