Clinical and dermoscopic features of combined cutaneous squamous cell carcinoma (SCC)/neuroendocrine [Merkel cell] carcinoma (MCC)

Abstract

Background: Merkel cell carcinoma (MCC) is a neuroendocrine carcinoma, associated with Merkel cell polyomavirus. MCC admixed with squamous cell carcinoma (SCC) is unassociated with polyomavirus, and is genetically distinct.

Objective: We sought to distinguish clinically and dermoscopically between MCC and SCC/MCC.

Methods: We compared patient data for SCC/MCC (n = 26) and MCC (n = 20), and reviewed clinical and dermoscopic images (n = 9) of SCC/MCC.

Results: Patients with SCC/MCC were older (median 76.5 vs 69 years) and more often male (77% vs 60%), and had more nonmelanoma skin cancer (85% vs 25%), malignant extracutaneous tumors (25% vs 5%), lymphoproliferative disorders (23% vs 10%), and immunodeficient/proinflammatory states (77% vs 35%). In all, 58% of SCC/MCC versus 10% of MCC were clinically diagnosed nonmelanoma skin cancer. Patients with SCC/MCC had more metastases (77% vs 40%), more treatment failures (53% vs 45%), shorter survival (41 vs 54 months), and more death from disease (50% vs 40%). SCC/MCC demonstrated marked scale (7/9), and telangiectasia (1/9). Dermoscopically, small dotted and short linear irregular peripheral vessels and central milky-red areas with large-diameter arborizing vessels were seen.

Limitations: The rarity of SCC/MCC limits available data.

Conclusions: SCC/MCC is aggressive, arising within elderly patients' chronically ultraviolet-exposed skin, often in the setting of immunosuppression or inflammation. Dermoscopically, polymorphous vessels in lesions suspicious for nonmelanoma skin cancer are suggestive.

Keywords: Merkel cell; biphenotypic; dermoscopy; neuroendocrine carcinoma; polyomavirus; ultraviolet signature.

Fig 1

Combined squamous/Merkel cell carcinoma. At low power, the biopsy specimen of the tumor from case 2 shows 2 distinct cell populations. The boundary of the tumors is distinct, the squamous component consisting of atypical pleomorphic keratinizing cells with squamous eddies (right arrow) and the neuroendocrine component consisting of a smaller round blue cell proliferation in the dermis (left arrow). (Hematoxylin-eosin stain; original magnification: ×40.)

Fig 2

Combined squamous/Merkel cell carcinoma, case 1. Scale-crusted nodule on the right temple (A). Intraoperative finding of a smooth, hard, erythematous subcutaneous nodule (arrow) (B).

Fig 3

Combined squamous/Merkel cell carcinoma, case 3. Erythematous nodule on the left temple with adherent yellow scale-crust (A). Intraoperative close-up examination, after scale-crust removed by curettage, reveals a smooth firm erythematous nodule (arrow) (B).

Fig 4

Combined squamous/Merkel cell carcinoma, case 2. An erythematous papule within a scar from prior basal cell carcinoma excision.

Fig 5

Combined squamous/Merkel cell carcinoma, case 4. An erythematous scaling nodule on the back of left wrist. Background dermatoheliosis with prominent telangiectasia, atrophy, and wrinkling, along with scattered solar lentigines.

Fig 6

Combined squamous/Merkel cell carcinoma, case 5. A, Erythematous nodule on the upper aspect of chest with adherent scale; background dermatoheliosis with atrophy and wrinkling, along with a nearby actinic keratosis (upper left corner). B, Dermoscopy with milky red areas centrally (small top arrow) and large-diameter arborizing vessels at the periphery (larger lower arrows).

Fig 7

Combined squamous/Merkel cell carcinoma. Dermoscopy from case 2 with central scale (large left arrow) and small dotted vessels at periphery (small arrows). Short linear irregular vessels are at the superior, right, and lateral aspect of the tumor (large top right arrow).