Rare basal cell metastasis of a basal-squamous skin collision tumour to the lung and axillary lymph node.

We report a case of a 60-year-old man who was a former cigar smoker with a slow-growing, large exophytic left shoulder mass (15 cm in diameter) and later found to have left axillary lymphadenopathy. Fine needle aspirate biopsy of the left shoulder mass revealed squamous cell carcinoma (SCC). However, pathology of the enlarged left axillary lymph node was reported as metastatic adenocarcinoma. The patient underwent surgical resection of the shoulder mass which comprised of SCC (>95%) and adenoid basal cell carcinoma (BCC) as a second component of the tumour. The BCC had identical histology as the metastatic carcinoma in the left axillary lymph node. Therefore, diagnosis was revised as cutaneous collision tumour with metastatic BCC. Six months later following adjuvant radiation therapy, the patient was diagnosed with metastatic BCC in the right lung. Stereotactic body radiation therapy (SBRT) and a selective hedgehog pathway inhibitor vismodegib were given with only limited efficacy. Clinical trial registration number NCT03132636.