Continued Increase in Melanoma Incidence across all Socioeconomic Status Groups in California, 1998-2012

Melanoma incidence has been increasing in light-skinned populations worldwide, but the reasons for the increase have been controversial. Our prior assessment in California non-Hispanic whites showed substantial increases in invasive melanoma incidence for tumors of all thicknesses in all neighborhoods categorized by socioeconomic status (SES) between 1988-1992 and 1998-2002. To understand whether these trends continued, we updated our assessment to include the diagnosis period 2008-2012 and more accurate pathologic stage at diagnosis. We used the California Cancer Registry to calculate age-adjusted incidence rates for over 58,000 newly diagnosed melanomas. Incidence rates not only continued to rise over the 10-year period from 1998-2002 and 2008-2012 but also showed significant increases in almost all groups defined jointly by tumor thickness or stage at diagnosis and a small area (census tract) SES measure. The largest relative rate increases were seen for regional, distant, and ulcerated disease, especially among males living in the lowest SES neighborhoods. Considering tumor thickness and stage as proxies for time to screening detection and neighborhood SES as a proxy for health care access, we interpret this pattern to indicate continued, true increases in melanoma occurrence as opposed to a thin tumor phenomenon simply driven by improved access to care.