De novo intraepidermal epithelioid melanocytic dysplasia: an emerging entity

MART-1-labeled melanocyte density and distribution in actinic keratosis and squamous cell cancer in situ: Pagetoid melanocytes are a potential source of misdiagnosis as melanoma in situ

BACKGROUND

Actinic keratosis (AK) and squamous cell carcinoma in-situ (SCCIS) within or near melanoma in situ (MIS) can complicate diagnosis due to overlapping clinical and microscopic features. This study aimed to describe basilar melanocyte density and pagetoid spread in AK and SCCIS for improved diagnostic accuracy.

METHODS

A total of 22 AK and 22 SCCIS biopsies containing a margin of uninvolved epidermis were immunostained with MART-1 (melanoma antigen recognized by T-cells 1). The basilar melanocyte:keratinocyte ratio and the number and distribution of pagetoid melanocytes were compared in AK, SCCIS, and uninvolved epidermis. An in-vitro human skin model was created to assess the impact of keratinocyte atypia on melanocyte distribution.

RESULTS

The median basilar melanocyte:keratinocyte ratio in SCCIS (1:11.49) was lower than in uninvolved epidermis (1:5.59, P = 0.0011), and the ratio in AK (1:6.94) was similar to uninvolved epidermis (P = 0.987). Pagetoid melanocytes were absent in perilesional skin but common in AK (21/22, P < 0.0001) and SCCIS (22/22, P < 0.0001). Pagetoid melanocytes at or above the mid-spinous layer were more common in SCCIS (21/22) vs AK (7/22, P < 0.0001). Pagetoid melanocytes were present in the in-vitro skin model made with neoplastic but not normal keratinocytes.

CONCLUSIONS

Pagetoid melanocytes in AK and SCCIS should be interpreted with caution to avoid overdiagnosis of MIS.

Morphologic clues and utility of fluorescence in situ hybridization for the diagnosis of nevoid melanoma

BACKGROUND

Nevoid melanomas include melanomas with a low power silhouette similar to melanocytic nevi. However, at higher power magnification, nevoid melanoma may have severe nuclear atypia and dermal mitoses.

METHODS

We performed a clinical, pathological and molecular study on a series of 58 examples of nevoid melanoma, excluding cases with spitzoid morphology.

RESULTS

We identified distinct morphologic patterns: 'classic' nevoid melanoma, superficial spreading melanomas with nevoid invasive melanoma, lentigo maligna with nevoid invasive melanoma and deep penetrating nevus-like nevoid melanoma. Fluorescence in situ hybridization (FISH) was positive in 74% of cases. Copy number gains in 8q24 were common in amelanotic nevoid melanoma. The median follow-up was 28 months (range 140). At last follow-up, 37 patients had no evidence of disease, 3 were alive with metastases and 6 died from metastatic melanoma. Of these six patients who died, four had a sentinel lymph node biopsy (SLNB) performed, which was negative in all four.

CONCLUSIONS

We describe distinct clues to the diagnosis of nevoid melanoma including occult intraepidermal atypia, and expansile nesting resulting in asymmetric silhouette or dermal papillae expansion. We also describe that nevoid melanoma have infrequent SLNB involvement in aggressive cases, and have frequent 8q24 gains rather than 9p21 deletions. Our results suggest that nevoid melanoma are distinct from spitzoid melanomas and should be distinguished.

Main clues in the pathologic diagnosis of melanoma: is molecular genetics helping?

Although conventional histopathologic examination is still the undisputable mainstay for the diagnosis of melanocytic skin neoplasms, application of molecular testing has experienced tremendous growth and will continue to expand in the future as the need for more specific diagnoses and new targeted therapies evolve. Ancillary molecular methods, including comparative genomic hybridization and fluorescence in situ hybridization, have the potential to provide important new information to challenging cases, and will help improve diagnostic accuracy, particularly in cases in which morphology is not conclusive. Pathologists are increasingly involved in the prospective genotyping of melanoma, which leads to patient stratification in light of the novel personalized therapeutic approaches in the advanced setting.