A 52-year-old male presented with a three-month history of a right anterior shoulder mass. The lesion had previously been surgically excised on two occasions; however, repeating surgical intervention was recommended. He denied any associated respiratory or constitutional symptoms, including cough or flu-like illness. His medical history was unremarkable, with no history of chronic medication use, and he had no known drug allergies. He was an active smoker.

Ultrasonography of the right axillary region demonstrated a thick-walled complex cystic lesion located along the anterior axillary wall. The lesion measured approximately 68 × 44 mm and contained thick fluid with associated internal granulation tissue, corresponding to an estimated volume of approximately 60 ml. No extension into the underlying musculature was identified, and there was no sonographic evidence of deep tissue involvement.

CT scan of the chest and abdomen with IV contrast showed partial visualization of the right shoulder region, with right axillary lymphadenopathy, the largest lymph node measuring 18 × 9 mm, demonstrating an intact fatty hilum with cortical thickening. The chest CT demonstrated clear lung fields and costophrenic recesses, apart from a small 5.5 mm dense pulmonary nodule in the anterior segment of the right upper lobe. No hilar or mediastinal lymphadenopathy was identified. There was no pleural thickening or pleural effusion. The heart and great vessels were unremarkable. The visualized skeleton showed no focal bony lesions, apart from degenerative changes. Abdominal CT findings were unremarkable,

Histopathological examination of the right anterior axillary mass revealed a poorly differentiated carcinoma consistent with sebaceous cell carcinoma. Microscopic evaluation demonstrated sheets of highly atypical pleomorphic cells with enlarged nuclei, prominent nucleoli, abundant clear to vacuolated cytoplasm, brisk mitotic activity including atypical mitotic figures, and areas of necrosis. Immunohistochemical staining supported the diagnosis, showing strong focal positivity for AE1/AE3 in approximately 40% of tumor cells, diffuse strong ring-like granular cytoplasmic positivity for adipophilin, and diffuse strong nuclear positivity for GATA3. The tumor cells were negative for ER, desmin, S100, ERG, and GCDFP15. The overall findings were consistent with a poorly differentiated sebaceous cell carcinoma involving the right anterior axillary region.

The patient underwent wide local excision (WLE) of the right anterior axillary mass under general anesthesia. Through an elliptical incision, the lesion was completely excised with circumferential (360-degree) resection margins. Sampling of the right axillary lymph nodes was also performed and sent for histopathological evaluation. Adequate hemostasis was achieved, and local flap reconstruction was performed. A Redivac drain was placed in the operative field, and the wound was closed in anatomical layers. The patient tolerated the procedure well, with no reported intraoperative complications.

Histopathology of the right anterior axillary wide local excision revealed a high-grade malignant neoplasm consistent with poorly differentiated sebaceous carcinoma with possible heterologous sarcomatoid differentiation, based on the histological findings and the preoperative immunohistochemical profile. The tumor measured 7 cm in greatest dimension with a maximum thickness of 7.5 cm and was predominantly located within the subcutaneous fat. All surgical margins were free of tumor, with the closest margin being the superior margin at 0.5 cm, and the deep muscle margin was uninvolved. Examination of 25 right axillary lymph nodes showed no evidence of metastatic tumor. There was no lymphovascular or perineural invasion, confirming complete excision of the primary tumor without regional lymph node involvement.

The patient had an uneventful postoperative recovery, with no major surgical complications. The wound healed satisfactorily, and there were no signs of infection, hematoma, or wound dehiscence. Given the diagnosis of high-grade poorly differentiated sebaceous carcinoma with possible heterologous sarcomatoid differentiation, the patient was advised to undergo close multidisciplinary follow-up with regular clinical examinations and appropriate imaging to monitor for local recurrence or distant metastasis. Long-term oncologic surveillance was recommended due to the aggressive nature of the tumor despite the absence of nodal involvement.