Basosquamous carcinoma (BSC)
Also known as metatypical basal cell carcinoma
Current theory is that basosquamous carcinoma is a rare variant of basal cell carcinoma with areas of differentiation into squamous cell carcinoma
This is supported by presence of transition zone- area of intermediate transition of atypia
Distinguished from “collision” tumors- which are discrete areas of BCC and SCC (both present in close proximity but as separate entities), more likely to lack a transition zone.
The diagnosis of BSC is important because of the increased likelihood of local recurrence and increased risk of metastasis
Incidence: estimated to account for less than 2% of skin cancers, however also suspected to be underdiagnosed (due to small biopsy specimens/ sampling of heterogeneic tumor, often histologic changes only apparent in deep layers)
Suspect cell of origin to be the pluripotent basal cell
Presentation:
Clinically indistinct from basal cell carcinoma
However more aggressive features, behaving more like SCC or other aggressive variants of BCC (local recurrence, lymph node involvement, distant metastasis) would suggest BSC
Majority present in the head and neck region, particularly midface region
Anatomic distribution of case series of 178 patients reported by Leibovitch was that commonly affected sites were the nose (33.1%), auricular area (18.5%), and periocular area (11.2%).
Diagnosis: Histologic. Importance of deep biopsy, as squamous differentiation may only be present in deep layers or perineurally.
-Basaloid cells which, in comparison to classic cells in BCC, are typically larger, mitotically more active and with increased apoptotic nuclei compared to BCC and with variable cytoplasmic keratinization. Less likely to have peripheral palisading or stomal reaction
-Transition zone with intermediate cells, fibroblasts, stroma
-Squamoid cells with cytoplasmic keratinization, dyskeratotic cells, frequent mitoses
Prognostic factors associated with recurrence: positive surgical margin, lymphatic invasion, perineural invasion, male gender, and tumor size (>2cm)
Treatment: wide local excision. No standardized treatment protocol. Clinical +/- radiographic evaluation for regional or distant metastasis. +/-adjuvant radiotherapy or chemotherapy depending on margin status, PNI, lymphovascular involvement, nodal involvement. Long term followup.
Click on photo to enlarge; advance to next with cursor over mid right border
Basosquamous Pathology Images | |||
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Cytokeratin 5/6 | Pan cytokeratin | ||
*Special thank you to Brian J. Howe, DMD for the pathology images
References:
Betti R, Crosti C, Ghiozzi S, Cerri A. “Basosquamous cell carcinoma: a survey of 76 patients and a comparative analysis of basal cell carcinomas and squamous cell carcinomas.” Eur J Dermatol. (2012). Electronic publication.
Costantino D, Lowe L, Brown D. Basosquamous carcinoma- an under-recognized, high-risk cutaneous neoplasm: Case study and review of the literature.” Journal of Plastic, Reconstructive & Aesthetic Surgery. 59.4(2006):424-428.
Leibovitch I, Shyamala C, Selva D, Richards S, Paver R. “Basosquamous carcinoma, treatment with Mohs micrographic surgery.” Cancer. 104. 1(2005):170-175.
Lima N, Verli F, Luiz de Miranda J, Marinho S. “Basosquamous carcinoma: histopathological features.” Indian J Dermatol. 57.5(2012):382-383.
Martin R, Edwards M, Cawte T, Sewell C, McMasters K. “Basosquamous carcinoma: analysis of prognostic factors influencing recurrence.” Cancer. 88.6(2000):1365-9.