Atypical presentations: SLNB may be warranted to rule out spitzoid malignant melanoma

Key Points

New York - The decision to perform a sentinel lymph node biopsy (SLNB) is sometimes made when there is concern about the malignant potential of a given lesion.

A recent study shows that nodal nevi can occur in the setting of Spitz nevi. According to one expert, SLNB is sometimes performed in the setting of diagnostically difficult spitzoid melanocytic proliferations under the premise of "treating" the worst-case scenario.

The finding of a benign melanocytic nevic deposit in an SLNB specimen could potentially lead to overdiagnosis of the atypical cutaneous lesion as definite metastatic melanoma.

Clinical study

In a recent study, three cases were presented with nodal nevi within SLNB of patients with Spitz nevi in a 10-year-old girl, 11-year-old boy and a 20-year-old woman. Each patient underwent SLNB because the spitzoid melanocytic proliferations were deemed "atypical" although they had been diagnosed by several pathologists as nevi.

"We did not find the chromosomal aberrations that are typical for melanoma upon examination by comparative genomic hybridization (CGH) in one of the cases. The other two cases have not undergone molecular studies.

"What was important about these proliferations is that they had the morphology, as well as, in one case, the chromosomal profile of a benign proliferation," says Melissa P. Pulitzer, M.D., department of pathology at Memorial Sloan-Kettering Cancer Center, New York, and lead author of the study.

The features that she looked for included location within the fibrous capsule or fibrous trabeculae of the lymph node, negativity or weak HMB-45 immunohistochemical staining, an absence of mitotic figures or Ki-67 labeling and bland cytology.

Within a nodal nevus, it is more reassuring to see an innocuous spindle cell morphology, as melanomas may tend to be more epithelioid in their morphology. Dr. Pulitzer concludes that these lesions were actually nevi with spitzoid features within the sentinel lymph nodes of patients who had atypical Spitz nevi at the primary cutaneous site.

SLNB was performed despite the opinion of expert pathologists that the cutaneous lesions were benign.

According to Dr. Pulitzer, there is a possibility that melanocytic proliferations, such as Spitz nevi, can drain to a lymph node via passive transport. The literature does support the notion that normal non-spitzoid nevi can be found in lymph nodes that drain regions of the skin that have acquired nevi and, in particular, congenital nevi.

Other studies have shown that patients who had undergone axillary dissection for breast carcinoma (nonmelanocytic tumors) were found to have nevi in their nodes.

"Sentinel lymph node biopsy has to be interpreted with caution, because there may be banal melanocytic deposits in the lymph nodes of patients with atypical Spitz tumors.

"In some cases, cytogenetics, as well as other ancillary studies, may have to be performed in order to determine whether or not these deposits are not nevi associated with a cutaneous atypical Spitz tumor, but possibly metastases of spitzoid melanoma," she says.

Controversial cases

A Spitz nevus in itself is a benign proliferation. However, there are borderline cases that have features of a Spitz nevus but appear atypical. The cases presented in this study were thought by at least one referring or consultant pathologist to exhibit borderline features.

When confronted with controversial cases, it is probably helpful or necessary to perform an SLNB if the cutaneous lesion appears malignant and suspicion is high, Dr. Pulitzer says.

In known melanoma that metastasizes, up to 10 percent of cases that have true lymph node metastases can also have lymph node nevi, so the presence of a lymph node nevus doesn't exclude concurrent metastatic melanoma in a nearby region of the node.

According to Dr. Pulitzer, each lesion must be evaluated individually, and the dermatologist should keep in mind the possibility that all lymph node melanocytic proliferations are not malignant.

Disclosure: Dr. Pulitzer reports no relevant financial interests.