A 73-year-old man presents for evaluation of an asymptomatic lesion on his chest noted several months previously. The patient is fair skinned, and his medical history is positive for both actinic keratoses and squamous cell carcinoma in situ. Examination reveals a 1.2-cm slightly hyperkeratotic plaque as well as scattered seborrheic keratoses.
Compiled by Lauren Ax, MSPAS, PA-C and Dr. Stephen Schleicher, MD
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Microscopic examination revealed an actinic keratosis arising in a seborrheic keratosis. The coexistence of 2 or more neoplasms with differing histology within a single cutaneous lesion is known as a collision tumor. Although some collision tumors may arise from similar cell lineages, other lesions arise inadvertently juxtaposed with small to no transition of cell types.1 Although relatively rare, it is even less common for intermingled collision tumors to occur with intimate mixing of the differing cell types.2 The most common collision occurs between basal cell carcinoma and benign nevus, basal cell carcinoma and seborrheic keratosis, or seborrheic keratosis and benign nevus.3
Pathogenesis of collision tumors is not well known. Noninvasive procedures such as dermoscopy and confocal microscopy may aid in clinical diagnosis. Appropriate therapy should be based in part on the histology.
1. Smith L, Hussain E. Colonisation of basal cell carcinoma and actinic keratosis by malignant melanoma in situ in a patient with xeroderma pigmentosum variant. Clin Pract. 2012;2(2):e47
2. Braun-Falco M. Combined malignant melanoma and basal cell carcinoma tumor of the intermingled type. J Cutan Pathol. 2007;34:731-735.
3. Boyd AS, Rapini RP. Cutaneous collision tumors. An analysis of 69 cases and review of the literature. Am J Dermatopathol. 1994;16:253-257.