DS20: Rising rates of melanoma in situ: a slowly growing problem?

C. Davies, S. Ogden, J. Newsham, A. Foulkes and A. Weidmann

Salford Royal Foundation Trust, Salford, UK

Melanoma in situ (MIS) is considered to be a precancerous lesion in which malignant cells are confined to the epidermis. The risk of developing malignant melanoma (MM) is approximately eight times higher in patients diagnosed with MIS than in the general population. There are few data concerning the incidence of MIS in the UK. Between 1993 and 2003, it was reported that the MIS incidence rates in Yorkshire (UK) were 2·1–2·5/100 000 in males and 3·2–3·4/100 000 in females. During that period, the rates of invasive melanoma had increased from 5·4 to 9·7/100 000 in males and from 7·5 to 13·1/100 000 in females (Downing A, Newton-Bishop JA, Forman D. Recent trends in cutaneous malignant melanoma in the Yorkshire region of England; incidence, mortality and survival in relation to stage of disease, 1993–2003. Br J Cancer 2006; 95: 91–5). We undertook a retrospective review of all patients diagnosed with MIS [International Classification of Diseases (ICD) code D03] and MM (ICD 43) in our local Clinical Commissioning Group (CCG; population of 291 500) between 2016 and 2020. In this period there were 192 cases of MIS, of which 43% were lentigo maligna. Annual age-standardized incidence rates of MIS showed no trend (mean 14·4/100 000; males 15·6/100 000; females 13·2/100 000). The mean age-standardized incidence rate of MM during the same period was 36·1/100 000. Anatomical distribution of MIS cases showed a similar gender distribution to other studies (males: head 39·4%, trunk 39·4%, limbs 21·2%; females: head 28·4%, trunk 20·5%, limbs 51·1%). Full-skin examination (FSE) is undertaken routinely in our department and 45% of MIS cases were diagnosed incidentally. The incidental diagnosis rate for MM was 28% during this period. We found that the incidence of MIS and MM in our area of the UK is much higher than that reported in Yorkshire between 1993 and 2003. Some of this may reflect trends in an upward incidence in MM as the age-standardized UK incidence of MM increased from 11/100 000 in 1993 to 25·9/100 000 in 2017 (Cancer Research UK Melanoma Statistics 2021). There are no comparative data for MIS. The annual age-standardized incidence of MM in our CCG (36·1/100 000) is significantly above the national UK incidence and we have detected more MIS relative to MM than in Yorkshire in 2003 (40% vs. 26%). We postulate that changing demographics, the success of public awareness campaigns, the use of dermoscopy (including in primary care) and the increasing use of FSE has contributed to increasing rates of MIS diagnosis. Rising case numbers are also indicative of increasing skin cancer prevalence. We continue to advocate for the use of FSE in dermatology and to champion the use of dermoscopy in aiding early diagnosis.