Differences in Thickness-Specific Incidence and Factors Associated With Cutaneous Melanoma in the US From 2010 to 2018

Key Points

Question  What patterns exist in the thickness-specific incidence of cutaneous melanoma in the US?

Findings  This population-based cohort study of 187 487 patients diagnosed with invasive cutaneous melanoma in the US between 2010 and 2018 found that overall and thinner melanoma incidence rates have stabilized, whereas the incidence of the thickest melanomas continued to increase. Individuals with lower socioeconomic status and members of minority groups were more likely to be diagnosed with thicker tumors.

Meaning  Findings of this study suggest that the incidence of the thickest cutaneous melanomas increased from 2010 to 2018, in contrast with thinner melanomas, and that overall melanoma incidence rates have potentially stabilized in the US after nearly a century of increase.

Importance  The recent incidence of cutaneous melanoma of different thicknesses in the US is not well described.

Objective  To evaluate recent patterns in the incidence of melanoma by tumor thickness and examine associations of sex, race and ethnicity, and socioeconomic status with melanoma thickness-specific incidence.

Design, Setting, and Participants  This population-based cohort study analyzed data for 187 487 patients with a new diagnosis of invasive cutaneous melanoma from the Surveillance, Epidemiology, and End Results Registry from January 1, 2010, to December 31, 2018. The study was conducted from May 27 to December 29, 2021. Data were analyzed from June 21 to October 24, 2021.

Main Outcomes and Measures  Age-adjusted incidence rates of melanoma were calculated by tumor thickness (categorized by Breslow thickness) and annual percentage change (APC) in incidence rates. Analyses were stratified by sex and race and ethnicity. The associations with socioeconomic status were evaluated in 134 359 patients diagnosed with melanoma from 2010 to 2016.

Results  This study included 187 487 patients with a median (IQR) age of 62 (52-72) years and 58.4% men. Melanoma incidence was higher in men compared with women across all tumor thickness groups. Individuals in lower socioeconomic status quintiles and members of minority groups were more likely to be diagnosed with thicker (T4) tumors (20.7% [169 of 816] among non-Hispanic Black patients, 11.2% [674 of 6042] among Hispanic patients, and 6.3% [10 774 of 170 155] among non-Hispanic White patients). Between 2010 and 2018, there was no significant increase in incidence of cutaneous melanoma across the full population (APC, 0.39%; 95% CI, –0.40% to 1.18%). The incidence of the thickest melanomas (T4, >4.0 mm) increased between 2010 and 2018, with an APC of 3.32% (95% CI, 2.06%-4.60%) overall, 2.50% (95% CI, 1.27%-3.73%) in men, and 4.64% (95% CI, 2.56%-6.75%) in women.

Conclusions and Relevance  In this population-based cohort study, the incidence of the thickest cutaneous melanoma tumors increased from 2010 to 2018, in contrast with the incidence patterns for thinner melanomas. The findings suggest potential stabilization of overall melanoma incidence rates in the US after nearly a century of continuous increase in incidence. Patients with low socioeconomic status and Hispanic patients were more likely to be diagnosed with thick melanoma. The continued rise in incidence of thick melanoma is unlikely to be attributable to overdiagnosis given the stability of thin melanoma rates.

Melanoma is the fifth most common cause of cancer in the US, with more than 106 000 expected new cases and 7000 estimated deaths in 2021.¹ Consistent increases in melanoma incidence documented since the 1930s show that melanoma incidence is now 6 times as high as it was 40 years ago.² It is unclear if this rising incidence is attributable to truly increased disease occurrence or overdiagnosis from frequent skin checks, biopsy results, and shifts in histopathologic criteria.² Tumor thickness is a crucial risk factor in melanoma, with a 10-year survival of 75% for the thickest (T4, >4.0 mm) compared with 98% for the thinnest (T1, ≤1.0 mm) tumors.³ Understanding incidence patterns by thickness, sex, race and ethnicity, and socioeconomic status is important in quantifying the true burden of melanoma in the US.

Melanoma incidence patterns by tumor thickness were formerly investigated through 2009.⁴ We investigated thickness-specific patterns in melanoma incidence by sex, race and ethnicity, and socioeconomic status.

In this population-based cohort study, histologically confirmed cases of first primary invasive cutaneous melanoma (International Classification of Diseases for Oncology, Third Edition codes 8720-8790 and topographic codes C44.0-C44.9) with malignant behavior were identified using data from the Surveillance, Epidemiology, and End Results (SEER) Registry for 18 population-based registries from January 1, 2010, to December 31, 2018. The study was conducted from May 27 to December 29, 2021. Data were analyzed from June 21 to October 24, 2021. Four categories of Breslow thickness were distinguished: T1, 1.0 mm or less; T2, greater than 1.0 to 2.0 mm; T3, greater than 2.0 to 4.0 mm; and T4, greater than 4.0 mm. Patient characteristics included sex, age, self-reported race and ethnicity, SEER summary stage, and histologic subtype. Area-level socioeconomic status defined by the Yost Index,⁵ a composite socioeconomic status measure based on Census tract–level information, was available from 2010 to 2016 across all registries except Alaska. Socioeconomic status was classified into quintiles, with Q1 as the lowest socioeconomic status and Q5 as the highest socioeconomic status. Annual incidence rates per 100 000 person-years were age adjusted to the 2000 US standard population. Patterns in incidence rate were examined using annual percentage change (APC) calculated using the weighted least-squares method and 1-year percentage change. Sensitivity analyses for assessing the implications of unknown thickness are outlined in eMethods 1, eResults, and eFigures 1 through 3 in the Supplement. Statistical calculations used SEER*Stat, version 8.3.9 (Surveillance Research Program, National Cancer Institute). Further methods are described in eMethods 2 and 3 in the Supplement. The Stanford Institutional Review Board deemed this study exempt from review and waived the requirement for patient informed consent because only deidentified data were used.

We identified 187 487 patients with newly diagnosed cutaneous melanoma from 2010 to 2018 (Table 1; eTable 1 in the Supplement). The patients had a median (IQR) age of 62 (52-72) years and included 109 500 (58.4%) men and 77 987 (41.6%) women, with 6042 (3.2%) Hispanic, 430 (0.2%) non-Hispanic American Indian or Alaska Native, 1145 (0.6%) non-Hispanic Asian or Pacific Islander, 816 (0.4%) non-Hispanic Black, and 170 155 (90.8%) non-Hispanic White patients (8899 patients [4.7%] were of unknown non-Hispanic race). Most patients, 75.1%, had thinner melanomas (T1 tumors, 116 952 [62.4%]; T2 tumors, 23 768 [12.7%]), 14.3% had thicker (T3 tumors, 14 728 [7.9%], T4 tumors, 11 928 [6.4%]), and 10.7% (20 111) had tumors of unknown thickness. Melanoma incidence was higher in men compared with women across all thickness groups. Patients from racial and ethnic minority groups were more likely to be diagnosed with the thickest (T4) melanomas (169 of 816 [20.7%] among non-Hispanic Black patients, 674 of 6042 [11.2%] among Hispanic patients) compared with non-Hispanic White patients (10 774 of 170 155 [6.3%]). Non-Hispanic White patients were more likely to be diagnosed with thin (T1) melanoma (106 099 of 170 155 [62.4%]) compared with Black patients (217 of 816 [26.6%]). Socioeconomic status data were available for 134 359 patients with melanoma. Individuals in lower socioeconomic status quintiles were more likely to have T4 melanoma compared with those in higher socioeconomic status quintiles (1157 of 11 304 [10.2%] in Q1 vs 1973 of 43 023 [4.6%] in Q5).

Table 2 shows melanoma incidence rates by thickness and sex in 2018 and the APC in incidence rate from 2010 to 2018. The overall incidence of melanoma did not increase significantly between 2010 and 2018 (APC, 0.39%; 95% CI, –0.40% to 1.18%). The incidence rate of melanoma in 2018 was 21.46 (95% CI, 21.17-21.75) for all tumors combined, 12.34 (95% CI, 12.12-12.56) for T1 tumors, and 1.56 (95% CI, 1.49-1.64) for T4 tumors. Incidence patterns differed by sex, with significant increases in incidence among women (APC, 0.92%; 95% CI, 0.01%-1.84%) but not among men (APC, –0.12%; 95% CI, –0.89% to 0.66%). From 2010 to 2018, there was a statistically significant increase in the incidence of T4 tumors (APC, 3.32%; 95% CI, 2.06%-4.60%), with similar patterns among men (APC, 2.50%; 95% CI, 1.27%-3.73%) and women (APC, 4.64%; 95% CI, 2.56%-6.75%) (Table 2).

The Figure shows incidence rates of melanoma by tumor thickness and sex for each year. For T1 through T3 melanomas, incidence rates peaked between 2013 and 2015 and then decreased until 2018. In contrast, the incidence of T4 tumors increased from 2010 through 2018 for both men and women. eFigures 4 through 6 and eTables 2 through 4 in the Supplement show incidence rate patterns and APCs by race and ethnicity, socioeconomic status, and age. For example, the APC for non-Hispanic White patients for the thickest (T4) tumors was 3.99% (95% CI, 2.89%-5.09%) (eTable 2 in the Supplement). Thin (T1) melanomas had an APC of 3.77% (95% CI, 0.63%-7.01%) for the lowest socioeconomic status quintile, and thick (T4) melanomas had an APC of 4.02% (95% CI, 1.92%-6.17%) for the second socioeconomic status quintile.

Using population-based SEER registry data for 187 487 patients with newly diagnosed cutaneous melanoma from 2010 to 2018, we assessed incidence patterns by tumor thickness, race and ethnicity, and Census tract–level socioeconomic status. We did not observe a significant increase in overall melanoma incidence; however, incidence for the thickest (T4) melanoma continued to rise with a significant APC of 3.32% between 2010 and 2018. This incidence differed from the pattern for thin (T1) melanoma, which peaked in incidence in 2013 through 2015 but steadily decreased since then. To our knowledge, this is the first study suggesting potential stabilization of melanoma incidence rates in the US after nearly a century of continuous increase in incidence.^2,6,7

Interestingly, melanoma incidence decreased in Hungary from 2016 to 2019, mirroring the pattern we noted in the US.⁸ However, melanoma incidence continues to rise in Australia, the United Kingdom, and Germany.^9-11 Although the overall melanoma incidence did not increase from 2010 through 2018, the continued increase of the incidence of thickest tumors during this period is concerning. Hispanic patients were more likely to be diagnosed with T4 melanoma compared with non-Hispanic White patients, suggesting persistent ethnic disparities.¹² Patients in lower socioeconomic status quintiles were also more likely to be diagnosed with T4 melanomas compared with those in higher socioeconomic status quintiles and are known to have worse melanoma survival outcomes.¹³ These differences by socioeconomic status cannot be solely attributed to racial and ethnic disparities, as non-Hispanic White patients accounted for 90.8% of cases.

The finding that populations with both lower socioeconomic status and racial and ethnic minority status were more likely to have thicker melanomas has important implications for melanoma risk awareness and health care access in these groups. Evidence suggests that teledermatology can successfully identify malignant lesions and can facilitate care, especially in rural populations and for those with reduced health care access.¹⁴ Advances in artificial intelligence algorithms show promise in improving real-time skin disease diagnoses in a teledermatology setting.¹⁵ As adoption of these novel technologies grows, it is important to ensure that they do not exacerbate health disparities.

Our finding of thinner melanomas among individuals with higher socioeconomic status suggests increased screening and detection among those with better health care access may contribute to overdiagnoses of biologically indolent tumors and could lead to an apparent increasing incidence of thin melanoma.² However, risk of thin melanoma is no longer increasing, and the increase in the incidence of the thickest melanomas suggests a true increase in the burden of prognostically worse melanoma cases in recent years.

This study has limitations. First, melanoma thickness data were unknown for 10.7% of patients, similar to past SEER analyses.⁶ Second, non-Hispanic Black patients were a small fraction of the total reported patients, limiting generalizability of results for non-Hispanic Black patients. Third, the composite socioeconomic status measure used may not reflect an individual’s characteristics because individual socioeconomic status may vary within Census tracts. Fourth, the lack of socioeconomic status information after 2016 reduced the sample size for socioeconomic status analyses.

This population-based cohort study is, to our knowledge, the first study to suggest potential stabilization of overall melanoma incidence rates in the US after nearly a century of continuous increase in incidence. However, the continued increase in incidence of the thickest melanomas is concerning. Members of racial and ethnic minority groups and individuals of lower socioeconomic status were more likely to have thicker tumors, which may contribute to health disparities. The continued increase in the incidence of thick melanoma is unlikely to be because of overdiagnosis given the stability of thin melanoma incidence rates.

Accepted for Publication: January 4, 2022.

Published Online: March 24, 2022. doi:10.1001/jamaoncol.2022.0134

Correction: This article was corrected on August 25, 2022, to change the article status to open access.

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2022 Chen ML et al. JAMA Oncology.

Corresponding Author: Eleni Linos, MD, DrPH, Department of Dermatology, Stanford University School of Medicine, 269 Campus Dr, Stanford, CA 94305 (linos@stanford.edu).

Author Contributions: Mr Chen and Dr Linos had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: Chen, de Vere Hunt, Linos.

Acquisition, analysis, or interpretation of data: All authors.

Drafting of the manuscript: Chen, de Vere Hunt, Linos.

Critical revision of the manuscript for important intellectual content: All authors.

Statistical analysis: Chen.

Obtained funding: Linos.

Administrative, technical, or material support: de Vere Hunt, Linos.

Supervision: Linos.

Conflict of Interest Disclosures: None reported.

Funding/Support: This study was supported by grants DP2CA225433 and K24AR075060 from the National Institutes of Health (Dr Linos). The study was the result of work supported with resources and the use of facilities at the Veterans Affairs Palo Alto Health Care System, Palo Alto, California, and the Providence Veterans Affairs Medical Center, Providence, Rhode Island.

Role of the Funder/Sponsor: The National Institutes of Health had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.