Abstract

Melanoma is an aggressive skin cancer with rising global incidence.While trends in invasive subtypes have been explored in some regions, no nationwide studies have documented them. This study examines incidence trends of most common subtypes in Iceland from 1955 to 2023, which include superficial spreading melanoma (SSM), nodular melanoma (NM), acral lentiginous melanoma (ALM), and lentigo maligna melanoma (LMM). Data from Icelandic Cancer Registry (ICR) were used to identify initial diagnoses, subtypes were classified using ICD-O-3 Morphology Codes, based on pathology subtype assigned at initial diagnosis by a pathologist, ensuring histologic confirmation. Sex-age-standardized incidence rates per 100,000 person-years were calculated, and Joinpoint regression analysis determined trends and annual percent changes (APC). 747 invasive melanomas were in men (41%) and 1,075 in women (59%). SSM incidence peaked at 6.15 in men (2007-2011) and 9.36 in women (1999-2003), followed by a decline. NM peaked at 1.53 in men (2001-2005) and 1.77 in women (1991-1995), with a recent increase in men (2016-2023, APC 12.03%). LMM peaked at 1.11 (2002-2004) and ALM at 0.63 (1986-1990). Breslow thickness for SSM had median of 0.80 mm (men) and 0.60 mm (women) (p<0.001), while for NM the medians were 2.65 mm (men) and 2.60 mm (women). This study found that SSM rose significantly among women, driven potentially by sunbed use; NM showed increasing rates among men; LMM remained stable, and ALM exhibited low but stable rates. Given the distinct biological and prognostic differences among melanoma subtypes, accurate subtyping is crucial for guiding effective prevention and management.