Collision tumour of trichofolliculoma and basal cell carcinoma

Multiple Skin Neoplasms at One Site (MUSK IN A NEST): A Comprehensive Review of Basal Cell Carcinoma and Benign or Malignant "Collision" Tumors at the Same Cutaneous Location

Multiple skin neoplasms at one site (MUSK IN A NEST), initially referred to as a collision tumor, describes the occurrence of two or more benign or malignant neoplasms that are adjacent or intermingled at the same cutaneous site. A mononeoplastic cutaneous tumor refers to a single tumor at any cutaneous site. Two, three, four, five, and six tumors at the same site are described as dineoplastic, trineoplastic, tetraneoplastic, pentaneoplastic, and hexaneoplastic cutaneous tumors, respectively; the prefixes are based on the numerical multiplier used by the International Union of Pure and Applied Chemistry (IUPAC). MUSK IN A NEST can be classified based upon their mechanism of pathogenesis-either being composed of mixed clones of cells (clonalium, which has three subtypes: collision, colonization, and combination) or the same clone of cells that has undergone clonal evolution (clonalidem, which has one subtype: biphenotypic). Basal cell carcinoma (BCC)-associated MUSK IN A NEST can be observed with either benign tumors, malignant tumors, or both. Nevi and seborrheic keratoses are the most common benign tumors associated with BCC; melanoma in situ and invasive melanoma are the most commonly reported malignant tumors associated with BCC. The definitive etiology of BCC-associated MUSK IN A NEST remains to be established-whether the development of the BCC at that site occurs as a direct or indirect consequence of the coexisting neoplasm or whether the occurrence of the BCC and the other neoplasm is merely the result of a coincidental juxtaposition of the tumors.

Clear Cell Hidradenoma-Basal Cell Carcinoma Collision

ABSTRACT

A 91-year-old man presented with a tumor on the left temporal area, clinically suspicious of basal cell carcinoma. The histopathologic study showed a central solid-cystic tumor composed by 3 different types of cells (clear or finely granular cells, polygonal cells, and squamoid cells). It had a sclerotic stroma. At the periphery, another tumor composed by smaller interconnected nests was evident. Some nests were separated from the stroma by clefts. The stroma of this second tumor was highly cellular. There was a sharp delimitation between both tumors, with no transitional area. Immunochemistry demonstrated they are different tumor. A diagnosis of clear cell hidradenoma-basal cell carcinoma collision was performed. To the best of our knowledge, this is the first description of this challenging association.

Review of the hair follicle origin hypothesis for basal cell carcinoma

BACKGROUND

Basal cell carcinoma (BCC) is the most common type of skin cancer treated by the dermatologic surgeon. The discovery that patients with the nevoid BCC syndrome had mutations in the human homologue of the Drosophila patched gene led to a rapid increase in our understanding of the pathogenesis of BCC. It is theorized that altered regulation at multiple steps in the patched signal transduction pathway may contribute to the development of BCC. This pathway also plays an essential role in embryonic hair follicle development and during the hair cycle. Taken together, a considerable body of evidence suggests that at least some BCC may be derived from deregulated patched signaling in hair follicle stem cells.

OBJECTIVE

To review evidence of a follicular derivation of BCC and to highlight emerging therapeutic strategies to block deregulated patched signaling in BCC.

CONCLUSION

Deregulation of the patched signal transduction pathway is present in the vast majority of human BCCs. Pharmacologic inhibitors of this pathway may offer a therapeutic strategy to block tumor growth. The author has indicated no significant interest with commercial supporters.