A Rare Collision in Dermatopathology: Basal Cell Carcinoma and Atypical Fibroxanthoma

A collision tumor of basal cell carcinoma and atypical fibroxanthoma: A case report

An 83-year-old man presented an elevated skin lesion in the left temporal area. The resected specimen was identified between a basal cell carcinoma and an atypical fibroxanthoma. A final diagnosis of basal cell carcinoma and atypical fibroxanthoma was made. This study reports a rare case of a cutaneous collision.

A Tale of Two Tumors: A Collision Tumor of Atypical Fibroxanthoma and Basal Cell Carcinoma

ABSTRACT

A collision tumor is an infrequent phenomenon characterized by the presence of 2 histologically distinct tumor types (either benign or malignant) occurring within the same specific anatomical site. We describe a rare case of co-occurrence of basal cell carcinoma and atypical fibroxanthoma presenting as a single lesion on the scalp in a 76-year-old man. The lesion was clinically suspicious for basal cell carcinoma and biopsied. Histologic examination showed 2 distinct tumors, one with basaloid cells and the other one with pleomorphic spindle cells colliding and growing together. Immunohistochemical stains were crucial in establishing the diagnosis. This presentation is exceedingly rare and requires additional evaluation for diagnosis.

Undifferentiated pleomorphic sarcoma in oropharyngeal mucosa of patients with multiple basal cell carcinomas

Malignant mesenchymal tumors of oropharyngeal mucosa are rare. Those with fibroblastic and histiocytic differentiation in the skin are called atypical fibroxanthoma (AFX) and in the soft tissue undifferentiated pleomorphic sarcoma (UPS). Here we present a case of an older patient with a history of multiple basal cell carcinomas and recently with a rapidly growing polypoid lesion in the mucosa of posterior oropharyngeal wall with AFX/UPS morphology. The differential diagnosis, histological pitfalls of this poorly characterized mesenchymal lesions, and the challenges associated with treatment are discussed.

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.

Collision tumors: A review of their types, pathogenesis, and diagnostic challenges

A collision tumor is a neoplastic lesion comprised of two or more distinct cell populations that maintain distinct borders. Collision tumors, which are rare but well documented, can be composed of two benign tumors, a benign and malignant tumor, and two malignant tumors. Although case reports and reviews on specific types of collision tumors exist, a cohesive source discussing these tumors is lacking. We critically reviewed the literature by analyzing case reports and retrospective studies in order to evaluate the following regarding collision tumors: definitions, types, pathogenesis, diagnosis, and management. Reports of these tumors are infrequent but not insignificant, and accurate classification and diagnosis will lead to better patient outcomes.

Atypical fibroxanthoma: An analysis of 105 tumors

Atypical fibroxanthoma (AFX) is a rare, low-grade dermal sarcoma. We analyzed our files from January 2001 to January 2020 for AFX. Clinical parameters, histopathology, treatment and outcome have been investigated. We identified 87 patients (mean age of 80.0 ± 8.4 years) with 105 confirmed tumors. Of these patients 86.2% were males. The most common clinical presentation was nodular (93.3%). The majority of AFX was located on the head with a mean tumor diameter of 15.0 mm ± 3.5 mm. All tumors showed a dermal localization, in 46.4% with a focal infiltration of the deeper layers. Second skin cancer was reported in 62.1% of patients. Collision tumors were seen in six patients. Treatment was surgical with three-dimensional margin control. Relapses were noted in 11.4% of tumors with a mean delay of 11.7 ± 17.3 months. Focally deeper infiltration of AFX was a risk factor (P = .014). None of the purely dermal AFX relapsed. No metastasis was observed. AFX is a rare mesenchymal tumor of elderly patients. Treatment of choice is the complete surgical excision. Due to the high rate of other skin malignancies among patients with AFX, a regular follow-up is recommended.