SAN FRANCISCO – Don’t recommend sentinel lymph node biopsy in patients with a melanoma depth of 0.75 mm or thinner unless there are true high-risk features, Dr. Susan Swetter advised at the annual meeting of the Pacific Dermatologic Association.
Increasing numbers of patients with thin melanomas being referred for consideration of sentinel lymph node biopsy inspired some revisions in the 2013 National Comprehensive Cancer Network melanoma guidelines regarding clinical stage, patient work-up, and treatment, said Dr. Swetter, professor of dermatology at Stanford (Calif.) University.
"Because of the issue of upstaging T1a and T1b melanomas based on the mitotic rate, we have seen a dramatic rise in cases referred to the academic centers for sentinel lymph node biopsy consideration," Dr. Swetter said.
Dr. Susan Swetter
The experts convened by the National Comprehensive Cancer Network (NCCN) in 2012 to revise the guidelines reviewed the evidence and found that thickness is the only consistent predictor of sentinel lymph node positivity for thin melanomas 1 mm or less in depth. They revised the stratification of stage IA and IB melanomas according to their risk for sentinel node metastasis rather than on the basis of the American Joint Committee on Cancer stage.
Essentially, tumors up to 0.75 mm in thickness have a low risk of metastasis (2%-2.5%) regardless of the mitotic rate. Tumors with a thickness of 0.76-1mm, particularly those with a high mitotic rate, have a higher risk of metastasis (approximately 5%), and are "very eligible" for sentinel lymph node biopsy, said Dr. Swetter, who was a member of the guidelines committee. "The 0.75-mm cutoff does not change the stage of the patient" but is a way of stratifying the risk for a positive sentinel node biopsy (J. Natl. Compr. Canc. Netw. 2013;11:395-407).
Guidelines from the American Academy of Dermatology in 2011 did not recommend sentinel lymph node biopsy for any T1a tumor up to 1 mm in depth because the AAD committee felt that the risk of a positive biopsy result should be at least 10% to justify the procedure, said Dr. Swetter, who also was on the committee that drafted those guidelines.
A key footnote in the NCCN 2013 recommendations: Sentinel node biopsy is not recommended for primary melanomas up to 0.75 mm unless there is significant uncertainty about the adequacy of microstaging, "meaning it’s a transected tumor or a nonrepresentative biopsy," Dr. Swetter explained. Sentinel node biopsy may be considered for melanomas 0.76-1 mm thick in the appropriate clinical context.
There is little consensus on what puts a thin melanoma (up to 1 mm) at high risk for metastasis, other than primary tumor thickness. Risk factors include a high mitotic rate (though the NCCN guidelines don’t specify a number), Dr. Swetter noted. Ulceration and lymphovascular invasion increase the risk but are rare.
"Consider sentinel lymph node biopsy in thin melanomas on an individual basis," Dr. Swetter said.
In general, don’t recommend sentinel lymph node biopsy for primary melanomas up to 0.75 mm thick unless there is a very high mitotic rate, lymphovascular invasion, ulceration, a nonrepresentative biopsy (with a large clinical residual lesion), or a partial biopsy (particularly one with deep transection of the tumor and inadequate microstaging), she said. A Clark level IV or V also might be cause for a sentinel node biopsy for a thin tumor, but "we only use Clark level when the mitotic rate can’t be assessed," she noted. "I can’t think of a case in the last 4 years where I’ve paid attention to the Clark level as a reason to pursue treatment in a patient."
One other "risk factor" for sentinel lymph node biopsy, even in a patient with a very thin melanoma and low mitotic rate, is a strong patient preference for the procedure, Dr. Swetter added. Dermatologists should try to educate patients and explain that their chances of a positive result may be fairly negligible, but if "they are determined to have sentinel lymph node biopsy, they will have it done," she said.
Dr. Swetter reported having no relevant financial disclosures.
On Twitter @sherryboschert