A Case of Pulmonary Basaloid Squamous Cell Carcinoma in a Non-Smoking Female: Case Report and Literature Review.

Pulmonary basaloid squamous cell carcinoma (BSCC) is a rare, high-grade subtype of lung squamous cell carcinoma. It predominantly affects elderly male smokers and is usually diagnosed at an advanced stage. Here, we report an early-stage BSCC in a 67-year-old non-smoking female identified during routine health screening. Chest CT revealed a 30-mm mass in the right lower lobe. PET-CT showed mild FDG uptake without lymph node or distant metastasis. Bronchoscopy confirmed malignancy, and thoracoscopic lobectomy with mediastinal lymph node dissection was performed. Gross pathology demonstrated a polypoid tumor protruding into the bronchial lumen. Histologically, the tumor exhibited solid basaloid nests with peripheral palisading and a high nuclear-to-cytoplasmic ratio. Immunohistochemistry showed strong p63 and CK5/6 positivity, with weak focal p40 expression in less than 20% of tumor cells. Ki-67 labeling index was approximately 50%. Neuroendocrine and breast cancer markers were negative. Mosaic p53 positivity was observed, and no actionable mutations were identified via next-generation sequencing. The final diagnosis was primary pulmonary BSCC (pT1cN0M0, Stage IA3). The patient remains recurrence-free 18 months postoperatively without adjuvant therapy. A literature review of 11 representative reports revealed BSCC typically presents in older male smokers at later stages and carries a poor prognosis. This case highlights the potential for BSCC to occur in non-smokers and at early stages, emphasizing the importance of a multidisciplinary diagnostic approach integrating histology, immunohistochemistry, and molecular data.