Multiple primary cutaneous melanoma (MPM) is defined as two or more independent melanoma lesion without attribution of metastasis or recurrence to each other’s presence. Histopathological differences, chronological orders, or negativity for metastasis work-ups indicate a possibility of MPM1. The presence of multiple primary acral melanoma is extremely rare. There are one case series of four MPM patients in African-American ethnicity, and one case has been reported in Korean patient123.

A 78-year-old Korean man referred to the dermatology clinic for the black and hyperkeratotic patch on his right heel (Fig. 1B). The lesion was first noticed 10-years ago. A punch biopsy of lesional skin was done at the center and it turned out to be an acral lentiginous melanoma in situ. He had another lesion on the left sole, which was 12 years old, diagnosed as melanoma 2 years ago and it was surgically excised (Fig. 1A; T4bN0M0, wide excision with full thickness skin graft). There was no radiological evidence of lymph node or visceral organ metastasis at that time, but now liver, lung, and chest wall metastasis was found on the radiological studies. He was referred to the hemato-oncology department for the palliative care, but refused all treatment options.

The right sole lesion occurred at the distant location from the left sole lesion, and there are pathological differences between the 2 melanomas: the excised right heel lesion shows only lentiginous spreading of atypical cells with no dermal invasion (Fig. 2C, D), but the left sole melanoma showed deeply invasive vertical growth with heavily pigmented melanoma cells (Fig. 2A, B). Therefore, it is plausible to conclude that the right side lesion is not the metastasis or recurrence of the left sole melanoma but another primary melanoma. One limitation is that we did not analyzed the excision specimen of the right sole lesion, because excision was not performed due to the extensive metastasis.

Acral lentiginous melanoma frequently occurs in oriental ethnicity24. However, MPM of acral site is exceedingly rare when comparing to the superficial spreading melanomas. Therefore, we performed cancer-specific high-throughput annotation of somatic mutations (CHASM) study for the both melanomas. The genetic mutation profile was negative for known KIT, BRAF, MEK, or NRAS gene mutations in melanomas. In recent study on multiple primary superficial spreading melanomas, CDKN2A gene mutation was statistically significant in these cases other than non-multiple melanoma cases5. Therefore, we suggest comparing genetic mutations in acral MPMs with solitary cases for the further studies.