A 59-year-old man presents for evaluation of a growth on his right shoulder. He states that the lesion has been present for at least 5 years but has significantly increased in size over the past 6 months. The patient denies experiencing any pain, discharge, or bleeding. His medical history is positive for psoriasis, psoriatic arthritis, hypertension, and hyperlipidemia. Physical examination reveals an erythematous, telangiectatic, fixed nodule. The patient’s cervical and axillary nodes are nonpalpable.
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Basal cell carcinoma (BCC) is the most common malignancy in the world with approximately 3.6 million new cases diagnosed each year in the United States.1,2 An uncommon, aggressive variant of BCC is basosquamous cell carcinoma (BSC), representing approximately 2.0% to 4.8% of skin cancers.3,4 The tumor has been referred to as mixed carcinoma, metatypical carcinoma, BCC with squamoid differentiation, keratotic BCC, and collision tumor variant.4
Clinical appearance is variable and dermatoscopic examination of the tumor is nonspecific.4 Diagnosis of BSC is made by histology with lesions demonstrating features of both BCC and squamous cell carcinoma.3 Once classified as collision tumors, BSCs are now believed to be BCCs that undergo squamous differentiation.4 A biopsy of the patient’s lesion confirmed BSC.
The majority of BSC cases occur on the head and neck of older males. Unlike BCCs, BSCs are aggressively invasive with a significant potential for metastatic spread and a high risk of recurrence. Treatment options include a wide surgical excision, Mohs’ micrographic surgery, and radiation therapy. For patients with unresectable or metastatic tumors, treatment with Hedgehog pathway inhibitors have shown promise.4
Renaldo Hidalgo, DO, is a family and sports medicine physician on staff of Allina Health in Minnesota. Stephen Schleicher, MD, is director of the DermDox Dermatology Centers, associate professor of medicine at Geisinger Commonwealth Medical College, and clinical instructor of dermatology at Arcadia University and Kings College.
1. Gualdi G, Soglia S, Fusano M, et al. Characterization of basosquamous cell carcinoma: a distinct type of keratinizing tumour. Acta Derm Venereol. 2021;101(1):adv00353. doi:10.2340/00015555-3710
2. Skin Cancer Foundation. Basal cell carcinoma overview: the most common skin cancer. Accessed March 9, 2022. https://www.skincancer.org/skin-cancer-information/basal-cell-carcinoma/
3. Betti R, Crosti C, Ghiozzi S, Cerri A, Moneghini L, Menni S. Basosquamous cell carcinoma: a survey of 76 patients and a comparative analysis of basal cell carcinomas and squamous cell carcinomas. Eur J Dermatol. 2013;23(1):83-86. doi:10.1684/ejd.2012.1890
4. Fotiadou C, Apalla Z, Lazaridou E. Basosquamous carcinoma: a commentary. Cancers (Basel). 2021;13(23):6146. doi:10.3390/cancers13236146