Primary Basal Cell Carcinoma Masquerading as Metastatic Basal Cell Carcinoma in the Left Axilla.

Basal cell carcinoma (BCC) is considered the most common malignancy in Caucasians. Despite its high prevalence, BCC has extremely low rates of metastasis. The patient was a 71-year-old male with extensive BCC and squamous cell carcinoma (SCC) skin cancer history who had an extensive, palpable left axillary mass concerning enlarged lymph nodes. No skin lesions were visualized. A lymph node biopsy revealed a sclerosing/infiltrative BCC with perineural invasion extending to the inked margins of the excision and one of four lymph nodes involved by BCC through direct extension. Sectioning revealed a 3.0 x 2.8 x 2.9 cm, ill-defined, fibrotic pink-white mass within the soft tissue. Two tan to pink possible lymph nodes were also identified within the soft tissue, measuring 0.7cm and 0.9cm. There was no definite direct invasion noted, making metastatic BCC suspicious. A left axillary lymph node dissection was performed. In short, he had a nonmobile tumor that showed evidence of invasion of the adjacent pectoralis muscle near the chest wall, abutting the left axillary vein, with extension. In July 2022, approximately one year after diagnosis, the patient received a PET scan and had no remote sites of disease. Every follow-up PET scan since has shown stable disease, most recently in May 2023. The patient continues dermatology follow-ups every three months for clinical surveillance. This case is unique because metastatic disease was never confirmed, though it is still a possibility. The affected lymph nodes were in the regional basin, where the patient had had extensive skin cancers in the past. Their involvement could have been secondary to direct invasion, though this could not be confirmed histologically, making the definitive characterization of this particular tumor difficult. As the PET CT scans have remained stable without evidence of distant disease, we favor that this is a recurrent primary tumor with direct extension to the underlying pectoralis and axillary lymph nodes. As common as BCCs are, this case highlights the importance of diligent treatment and follow-up to avoid the potential for tumor-related morbidity and, rarely, mortality.