Melanoma FISH?

Skin cancer is the most common type of cancer in the United States, and melanoma is its deadliest form. The American Cancer Society estimates that more than 68,000 new cases of melanoma were diagnosed in 2010 with 8,700 deaths.

In some patients, melanoma can be difficult to diagnose by pathologists because some benign nevi (a type of noncancerous mole) can display microscopic changes that mimic melanoma to the pathologist interpreting the tissue slides. A test, known as the fluorescence in situ hybridization (FISH) molecular assay, helps to distinguish these borderline cases by looking for DNA abnormalities. These abnormalities appear in the vast majority (95%) of melanomas but are not seen in benign nevi, making the melanoma FISH test an important extra step in the diagnosis of melanoma in cases with ambiguous or borderline microscopic findings on biopsy.

The importance of taking this extra diagnostic step is illustrated by the case of a 15 year-old girl who presented to her dermatologist’s office with a worrisome mole on her shoulder. The resultant biopsy displayed difficult-to-classify microscopic changes that suggested a possible malignant melanoma arising within a benign nevus (cancer arising from a previously noncancerous mole).

A melanoma FISH test was performed at Miraca Life Sciences. Using FISH to evaluate the entire mole, dermatopathologists and cytogeneticists discovered mutations only in the superficial layers and junctional components of the tumor and not in the deeper area of the nevus, confirming an early invasive melanoma arising in a pre-existing nevus, rather than a level IV melanoma or a totally benign nevus.

This was good news for the patient. While the application of the melanoma FISH test confirmed the suspicion for malignant melanoma (not a diagnosis easily made in a patient this age), it also allowed accurate measurement of depth of invasion, sparing the patient unnecessary sentinel lymph node surgery, while ensuring that she received a wide excision for melanoma.

Because these atypical, complex melanocytic tumors are often over- or under-diagnosed, the importance of a diagnostic tool like the melanoma FISH test are obvious. Cutting edge pathology laboratories use melanoma FISH testing to ensure the precision of these diagnoses and help guide the most appropriate treatment. Tests like these, when applied judiciously, can have tremendous benefit to patients and the physicians responsible for their care.