Rates and timing of sentinel node biopsy for melanoma under the microscope

Skin cancers

By Mardi Chapman

16 Mar 2022

The time interval between diagnostic excision of melanoma and sentinel node biopsy (SNB) does not impact the SN-positivity rate or survival, new studies show.

According to data from a Dutch population-based cohort of 7,660 melanoma patients and an independent cohort of 3,478 patients from Melanoma Institute Australia, the median time to SNB was 36 and 27 days respectively (range 1-100 days).

A study, published in the European Journal of Cancer, found no significant survival differences in either cohort based on whether SNB was performed during the first, second or third month after diagnostic excision of their primary melanoma.

“There was no significant association between time to SNB and RFS or OS in multivariable analyses (analysed either continuously and categorically) for either of the two cohorts, when adjusting for SN status, sex, Breslow thickness, age, primary site, ulceration, and mitoses,” it said.

The study also found patients in whom SNB was performed in the second or third month had no greater chance of SN-positivity than patients who had SNB during the first month.

“It could be argued that the most important time interval is between melanoma development and when the patient consults a physician or a physician diagnoses the melanoma,” it said.

However another study from the same cohorts found some evidence that the time interval to SNB affected the size of metastatic tumour deposits in positive nodes.

In the Dutch cohort, it found that the SN metastasis diameter was 0.6 mm when the SNB was performed during the first month after diagnostic excision, 0.7 mm when performed during the second month and 1.2 mm when performed during the third month.

The same effect was not seen in the Australian cohort.

The researchers suggested delaying SNB by a few weeks “may be largely inconsequential compared with the latency between the malignant transformation of a pre-malignant lesion into melanoma and its diagnosis.”

However, “The results of this study have important clinical implications if the size of SN tumour deposits is to be used as a criterion for recommending adjuvant systemic therapy,” it concluded.

An unrelated study published in The MJA this week suggests that, regardless of timing, SNB may be underutilised in Australia compared to recommendations.

In an analysis of SNB rates in Victoria during the 2018 and 2019 calendar years, it found 48% of patients diagnosed with invasive melanomas of > 1.0 mm thickness and 25% of patients with melanomas of 0.8–1.0 mm thickness underwent SNB.

Overall, 20% of SNB results were positive. Younger people <60 years were more likely to have SNB performed than older people (21% v 17%) and more likely to have positive nodes (23% v 17.6%).

“Our findings suggest that the use of SLNB has not increased in Australia beyond previous reports, despite the availability of effective systemic therapy,” it said.

This is consistent with a 2021 survey of dermatologists which found a significant proportion were unsure about the value of SNB or disagreed with recommendations.

“The optimal use of online risk tools in practice, and barriers to patient access to SLNB, should be investigated,” The MJA study concluded.

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