Residual melanoma is rare in wide local excisions (WLE) post complete excision biopsy (CEB), but the practice is still important for preventing local recurrence, according to Australian researchers.

A study of 640 patients with in situ or invasive melanoma excised between 2013 and 2015 found only 20 (3.1%) had residual disease upon WLE.

Of these, 15 had residual melanoma in situ, though 12 were originally diagnosed with invasive disease, the authors wrote in Anatomical Pathology.

Three of the remaining five patients had tumours in or next to the scar, while the other two had clinically-detected in-transit metastasis, and microsatellites, lymphovascular invasion and tumour in the scar.

“While most residual disease occurs in the form of melanoma in situ and is unlikely to be clinically significant, rare cases of residual invasive disease (<1% in our study) are detected and occasionally these could have management implications for individual patients,” the authors wrote.

Residual disease detection likely affected one patient’s eligibility for adjuvant drug therapy, however, a previous study showed no relationship between residual melanoma in WLE specimens and disease-free or overall survival after 5 years’ follow-up, they noted.

Patients were most likely to have residual disease if they had lentigo maligna (LM)/LM melanoma, nodular melanoma, or invasive tumours with a higher mitotic rate, Breslow thickness >4 mm, larger primary lesion and amelanosis.

“This study confirms that the finding of residual disease in WLE specimens performed within standard timeframes [less than six weeks] is an infrequent occurrence (3.1% in our study). WLE after CEB remains an important procedure to reduce local recurrence,” they concluded.

The findings would also have important implications for laboratory resources, they added, given that several studies have now shown that exhaustive histological examination of WLEs after an original excisional biopsy with negative margins is of limited value.

“On the basis of our study’s findings, melanomas of LM/LMM and NM subtypes, higher mitotic rate, Breslow thickness >4 mm, larger lesion diameter and amelanosis probably warrant additional sampling of WLE specimens,” they suggested.