Colliding, colonizing or combining? Four cases illustrating the unique challenges presented by melanoma arising in conjunction with basal cell carcinoma

Abstract

Biphasic lesions comprised of melanocytic and epithelial components are rare entities believed to arise either as a collision of 2 histologically distinct lesions in the same anatomic location or as a singular progenitor tumor differentiating along 2 differing lineages. Regardless of mechanism of origin, these tumors present unique challenges in pathologic interpretation and in determining appropriate measurements, which assigns subsequent prognosis to the patient. We present 4 tumors of melanoma co-existing with basal cell carcinoma (BCC) and discuss relevant literature regarding these biphasic entities. Patients consisted of 3 males and 1 female, ranging in age from 62 to 93, with lesions located on the shoulder, frontal scalp, forearm and nose. Three of 4 lesions showed melanoma cells limited to BCC tumor lobules, without evidence of direct dermal invasion by melanoma cells, raising the question of whether or not these tumors should be classified as in situ or invasive melanoma. These cases highlight the complexity that such lesions pose to dermatopathologists, in terms of their uncertain origin and variable microscopic appearance. In the absence of data regarding outcomes for these tumors (given their rarity), it is important to utilize a case-by-case approach, with careful clinical correlation and appropriate use of ancillary techniques.

Cutaneous neoplasms composed of melanoma and carcinoma: A rare but important diagnostic pitfall and review of the literature

“…Combined tumors are defined as neoplasms composed of two phenotypically distinct yet intermingled cell populations, for which the use of immunohistochemical studies is usually required to highlight the two distinct cell populations . Overlap between these tumors may occur in which tumors show a mixed pattern that can fall into both collision and combined categories . Colonized tumors develop when one type of tumor cell population permeates but remains within a second tumor .…”

<p>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</p>

“…These included (ranging from the two neoplasms being the least admixed to the most admixed) collision, colonization, combination, and biphenotypic tumors. 64,82 A collision tumor refers to two independent cutaneous neoplasms that are contiguously next to each other at the same anatomic site. Colonization refers to a tumor in which one distinct neoplasm (such as melanoma in situ) has infiltrated a second distinct neoplasm (such as a BCC); however, the infiltrating neoplasm is confined only to the second neoplasm without any invasion into the adjacent dermis.…”

“…A biphenotypic tumor refers to a tumor that initially originates from the same stem cell or single clone of cells and subsequently differentiates into two neoplasms that are phenotypically distinctive; hence, neoplasms of the tumors have common genetic, ultrastructural, and immunohistochemical features. 64,82 After completing our assessment of the literature, we propose that a classification of MUSK IN A NEST that is based upon the postulated mechanism of pathogenesis will enable a better understanding and categorization of these tumors. Hence, we have created primary categories based on whether there are mixed clones (clonalium) or clonal BCC, nevus (blue), speckled lentiginous nevus 43 BCC, nevus (compound or intradermal), seborrheic keratosis 32,45 BCC, nevus (intradermal), melanoma in situ 46 BCC, nevus sebaceus, syringocystoadenoma papilliferum 4 BCC, nevus sebaceus, trichoblastoma 80 BCC, nevus sebaceous, squamous cell carcinoma 81 BCC, porokeratosis, squamous cell carcinoma 24 evolution (clonalidem).…”

“…31 A similar hypothesis proposed for the development of melanocytic tumors at the same site as a basal cell carcinoma-and described as the interaction theory-suggests that the unrestrained growth of the neoplastic cells and melanocytic tumor result from BCCinduced increased growth factors and cytokines in that area of skin. 64 The third theory is that of a field cancerization phenomenon. In an anatomic skin location where the two neoplasms typically develop, exposure to ultraviolet radiation or another environmental carcinogen primed the cutaneous site and thereby enhanced the chance for both to concurrently appear at the same cutaneous location.…”

“…The information provided in the reports of the remaining 17 patients was not sufficient to allow them to be classified. 64 The prognosis and treatment of melanoma is based on the Breslow thickness depth of invasion. For patients with BCC-associated MUSK IN A NEST and melanoma, in whom the invasive melanoma is present peripheral to the BCC, the melanoma depth can be measured in a standard fashion.…”