Acral lentiginous melanoma (ALM) has significantly poorer survival than other melanoma types, according to new Australian research published in the British Journal of Dermatology.

The study comprised almost 3,000 invasive cutaneous primary melanoma cases – 101 ALMs, 2,272 superficial spreading melanomas (SSM) and 578 nodular melanomas (NM) – seen at the Victorian Melanoma Service between 1994 and 2016.

Cases were reviewed by an expert melanoma dermatopathologist and survival determined via linkage with the Victorian Cancer Registry.

Adverse pathological features such as lymphovascular invasion and neurotropism were more apparent in ALM than the other two melanoma subtypes, the researchers noted.

The median mitotic rate was fourfold higher in ALM than SSM and the rate of hypomelanosis was also greater in ALM than SSM but low compared to NM.

Breslow thickness was highest in NM, then ALM and lowest in SSM.

When adjusting for the five clinicopathologic variables, melanoma specific survival (MSS) was higher for superficial spreading melanomas (HR 0.70) and nodular melanoma (HR 0.50) compared to acral lentiginous melanoma.

The study authors – led by Dr Matthew Howard – said the findings should be seen in the context of ALM typically being diagnosed at an advanced stage, perhaps due its unique presentation.

“Our findings of poorer adjusted survival of ALM patients compared to NM suggest that ALM may have more high risk biology, in keeping with the higher rate of lymphovascular invasion in our study and another series.”

“Genetic difference between ALM and MM may underpin distinct tumour biology and clinicopathologic differences,” the researchers said.

However mutational status was not assessed, as molecular testing was incomplete for older cases in the series.

The study also found ALMs were significantly more common in females (55.4%) compared to NM (38%).