Long term monitoring essential for lentiginous melanoma

Skin cancers

By Mardi Chapman

3 Feb 2021

Dr Helena Collgros

A ten-year follow up of lentiginous melanoma in Australia has confirmed a high rate of late recurrence reinforcing the importance of long-term follow-up of patients.

The retrospective study comprised a review of medical and imaging records of 102 patients with lentiginous melanoma in situ or invasive lentiginous melanoma managed at a tertiary centre in Sydney.

The study, published in JEADV, found a recurrence rate of 38% over a mean follow-up of 7.5 years. The median time from treatment to recurrence detection was 3.8 years.

Among patients with a recurrence, 50% had a single recurrence; 23% had two recurrences, 14% had three recurrences, 7% had four recurrences and 7% had six recurrences.

“When considering together the 50 cases with recurrence or treatment failure after the first treatment, the median time until a recurrence or further treatment was 3.3 years (95% CI 2.0-4.2), and this interval decreased as the number of recurrences or treatments increased, subsequently to 1.7 years (95% CI 0.5-3.7) and 0.5 years (95% CI 0.2-4.1),” the study said.

Nearly all (97%) of primary lesions were initially excised with a mean histological clearance of margins of 4.9mm.

“Current guidelines recommend clinical excision margins of 5-10mm for melanoma in situ and several studies have recently shown that up to 10mm clinical margins are needed to clear most cases of LM.”

The investigators said the narrow margins reported in their series might be explained by the typically subtle appearance and ill-defined peripheral margins of these lesions.

As well, it was difficult to perform wider excisions in cosmetically sensitive areas such as the face, and particularly in elderly patients.

The study found that while 71% of primary lesions were pigmented, only 11% of recurrent lesions were pigmented.

“New techniques, such as reflective confocal microscopy (RCM), may improve the accuracy of diagnosis, evaluation for an invasive component and margin involvement, treatment planning and follow-up of lentiginous melanomas.”

Lead investigator Dr Helena Collgros, from the Sydney Melanoma Diagnostic Centre, told the limbic that lentiginous melanoma was increasing in incidence.

However it was easily missed and sometimes mismanaged when treated cosmetically with laser.

“A high percentage are very lightly pigmented – about one-third of cases have just partial pigmentation – and most people think it is just an age spot.”

“I have seen many patients who see the dermatologist to have an age spot removed because of cosmetic reasons and then we realise it is not an age spot but a melanoma. And sometimes you have a combination of an age spot  and the melanoma in one area.”

She said anything slightly suspicious on dermoscopy should be referred to a centre with RCM.

“It’s particularly helpful for these large spots on the face where you don’t want to be biopsying. RCM can scan the whole lesion and if you see some atypia in one area, then you just do a targeted biopsy.”

She said LM patients will require long-term follow-up.

“For most melanomas we say that the main danger is during the first two years so we encourage patients to come often to the clinic. But we know that most of these lentiginous melanomas will recur after three years so it is important to follow-up for 5-10 years or forever. A very high percentage of them will come back and they will come back late.”

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