SAN FRANCISCO –
The finding supports the 2017 revision in the American Joint Committee on Cancer guideline, which dropped mitotic rate from its criteria for upstaging thin melanomas.
An earlier version of the guideline, published in 2010, had called for upgrading thin (less than 1 mm), nonulcerated melanomas with a mitotic rate (MR) of at least 1/mm2 to T1B, which could then trigger an SLN biopsy.
SLN biopsy is controversial in thin melanomas, because there is no evidence that it has a survival benefit in these populations, though it is useful as a prognostic measure. However, the procedure carries a risk of complications.
“This makes judicious selection of patients for the procedures even more important,” Heidi Wat, MD, of the division of dermatology at the University of Alberta, Edmonton, said during her presentation of the research at the annual meeting of the Pacific Dermatologic Association.
The researchers set out to determine the predictive value of mitotic rate (the number of cells undergoing cell division) on SLN status, particularly when stratified by tumor thickness. They analyzed 990 SLN biopsy procedures performed in Alberta from January 2007 through December 2013, which were pulled from the Cancer Surgery Alberta tumor database and provincial pathology records. The mean age of the patients was 57 years (range, 15-93 years), and 55% were male; 171 records involved thin melanomas.
Overall, 25.4% of SLN biopsies came back positive, including 8.8% of thin melanomas. Among all cases, there was a statistically significant association between a mitotic rate of 1 or higher and a positive SLN biopsy.
However, when the researchers stratified the results by thickness, they found a statistically significant association only between mitotic rate and SLN biopsy positivity in thicker tumors (1-2 mm, P = .01).
Further analysis of factors including age, ulceration, and tumor location showed that MR and thickness measures were not independent, and the potential for MR to predict SLN biopsy positivity declined at lower thickness values.
“Performing sentinel lymph node biopsy in thin melanomas upstaged purely because of the finding of a single mitotic (event) has questionable clinical value,” said Dr. Wat.
The 2010 AJCC guidelines called for upgrading thin tumors with an MR of 1 or higher, or ulceration, to T1b. The new AJCC guidelines restrict the definition of T1b to tumors 0.8-1.0 mm in size with or without ulceration, or tumors 0.8 mm or smaller with ulceration.
“The results really confirm,” said , of the department of dermatology at the University of California, San Francisco, who chaired the session in which the research was presented.
SLN status remains a useful prognostic indicator, Dr. Wat said, and MR may still be useful for intermediate and thick melanomas.
Dr. Wat and Dr. Botto reported no relevant financial disclosures.