Poster Presentation Australasian Melanoma Conference 2018

Primary dermal melanoma - a description of a patient cohort at an Australian tertiary centre  (#129)

Louise Photiou 1 , Nikki R Adler 2 3 , Andrew Haydon 1 4 , Catriona A McLean 5 , John W Kelly 1 , Victoria J Mar 1 3 6
  1. The Victorian Melanoma Service, The Alfred Hospital, Vic, Melbourne
  2. St Vincent’s Hospital, Melbourne, Vic, Australia
  3. School of Public Health and Preventive Medicine, Monash University, Melbourne, Vic, Australia
  4. Department of Medical Oncology, Alfred Hospital, Melbourne, Vic, Australia
  5. Department of Anatomical Pathology, Alfred Hospital, Melbourne, Vic, Australia
  6. Skin and Cancer Foundation, Carlton, Vic, Australia

Background: Primary dermal melanoma (PDM) represents melanoma confined to the dermis without an epidermal (junctional) component. At the histologic level, it is often difficult and sometimes impossible to distinguish between PDM and cutaneous metastasis. This differentiation mostly relies on thorough clinical history, examination findings and clinicopathological correlation. However, this differentiation is very important as it confers significant prognostic and therapeutic implications. That is, the prognosis and treatment for a primary melanoma differs significantly from that of an American Joint Committee on Cancer (AJCC) stage IIIC or stage IV M1a metastatic melanoma. Therefore, this distinction is critical. The aim of this study was to describe the clinical and pathological characteristics of a cohort of patients with presumptive PDM.

Methods: This was a retrospective review of all patients who presented with a PDM between 2006 - 2016 to a single tertiary referral centre in Melbourne, Australia.

Results: We identified 61 patients with a diagnosis of PDM defined clinically as no previous history of a primary melanoma, and/or pathologically as a tumour confined to the dermis with no reported epidermal (junctional) component, no in-situ component and/ or the question as to whether it was a metastasis raised in the pathology report. The median age at diagnosis was 66 years (range 33 - 94). The majority of lesions were found on the trunk (n=26, 35%). Almost half of the lesions (n=36, 48%) were considered amelanotic. The median Breslow thickness was 4.1mm (range 0.5 - 18). The median number of mitoses was 7.5. Twenty three patients out of a potential 56 eligible patients underwent a sentinel lymph node biopsy with four reported positive. One patient had stage IV disease at presentation. Fifteen patients underwent baseline scanning with PET-CT +/- CT with metastases reported in 4. Eleven patients developed clinically detectable nodes over a range of 1 - 88 months (median 20) and underwent nodal dissection. Positive nodes were found in 13 patients with a median maximum size of 30.6mm (range 8-70) and 5 had extra-capsular extension. Ten patients developed local recurrences. Six patients developed distal metastases over a median of 50.5 months (range 9 - 115) including distant nodes, subcutaneous nodules, muscle, lung, spleen, bone, liver, and brain. Four patients developed further primary melanomas. Thirty-two patients underwent molecular genetic testing of which 8 were found to have a BRAF mutation, 5 had an NRAS mutation, and none had a c-KIT mutation.

Conclusion: This study describes a group of patients with presumptive PDM from a tertiary referral centre in Australia.