Adenoid-Type Basal Cell Carcinoma on the Anterior Chest Wall: A Rare Histopathological Variant in a Non-Sun-Exposed Area (Preprint)

BACKGROUND Basal cell carcinoma (BCC) is the most common form of skin cancer, primarily affecting sun-exposed areas such as the head and neck. However, non-sun-exposed locations account for a minority of cases. The adenoid subtype of BCC is an uncommon histological variant with glandular-like structures and cystic spaces. This report presents an unusual case of adenoid-type BCC occurring on the anterior chest wall, a rarely reported site, emphasizing the importance of recognizing atypical presentations of BCC. OBJECTIVE To report a rare case of adenoid-type basal cell carcinoma (BCC) occurring in a non-sun-exposed area, specifically the anterior chest wall, and to highlight its clinical, histopathological, and immunohistochemical characteristics. This case aims to contribute to the understanding of atypical presentations of BCC and reinforce the importance of considering histopathological evaluation in unusual skin lesions. METHODS A 53-year-old male, a farmer by occupation for more than 15 years, presented with a gradually progressive non-itchy, painless mass on the anterior chest wall noticed two years before which bleeds with minor injury/trauma. There was no previous personal or familial history of skin cancer and no other significant medical history was elicited. Basal Cell Carcinoma (BCC) is the most frequent type of malignant skin tumor, with 80% of cases involving the head and neck region and only a small percentage involving the trunk and limbs. RESULTS The wide local excision of raised and ulcerated tumor having size of 2*1.8 cm was made. Histologic examination of the mass showed basaloid neoplasm, a feature consistent with basal cell carcinoma, nodulocystic and adenoid type. Lobules of neoplastic basaloid cells with peripheral nuclear palisading were seen with scattered mitotic figures. Depth of the lesion was 0.4cm. Lymphatic, vascular, perineural invasion were not identified. Margins were free of tumor; nearest lateral margin was 0.5cm and the deep margin was 1.2cm. According to the TNM tumor, nodes and metastases) staging system, it was classified as pT1b stage (tumor size 2cm or less in greatest dimension). The tumor was limited to dermis, more than 2mm and less than 6mm in thickness. Hence, the skin biopsy showed the pathological diagnosis of basal cell neoplasm in favor of BCC. CONCLUSIONS This case highlights an atypical presentation of BCC in a non-sun-exposed area, underscoring the need for clinical vigilance in diagnosing and managing rare variants. Awareness of such uncommon locations expands the diagnostic spectrum of BCC and ensures timely intervention.