Keratinocyte Cancers Most Commonly Located on the Head and Neck, US Study Finds

A large Medicare cohort study published in JAMA Dermatology determined that the most common locations of procedurally treated keratinocyte cancers in the US were the head and/or neck for both squamous cell carcinomas (SCCs) and basal cell carcinomas (BCCs), followed by the upper limbs and trunk for SCCs and BCCs, respectively.¹

The study was the first report on keratinocyte locations in a large claims data set in the US, according to the authors. The findings highlight the anatomic locations of keratinocyte carcinomas in recent years and may help improve risk factor differentiation and surveillance for skin cancer.

“Information regarding anatomic locations of keratinocyte carcinomas is primarily based on single-center cohorts outside of the US. Keratinocyte carcinomas are not included in US national cancer registries (email communication, National Cancer Database, February 8, 2023), and information on the anatomic locations of keratinocyte carcinomas in the US is lacking,” the authors wrote. “Information on the relationship between anatomic location of keratinocyte carcinomas and patient demographics is limited.”

Skin cancer check | Image credit: InsideCreativeHouse - stock.adobe.com

Keratinocyte carcinomas are the most frequently diagnosed cancers among fair-skinned populations, with the main driver of these cancers being ultraviolet radiation exposure.² Cutaneous SCCs and BCCs are keratinocyte carcinomas, and although these cancers are the most frequently diagnosed in the Western world, their precise incidence worldwide is not known.

In the Medicare cohort study, authors used a deidentified, random sample of 100% Medicare claims data from 2009 to 2018.¹ The data encompassed 4,999,999 beneficiaries who had continuous Medicare Parts A, B, and D coverage and who did not have Medicare Advantage. Beneficiaries with at least 1 procedurally treated keratinocyte carcinoma—defined as at least 1 Current Procedural Terminology (CPT) code for a keratinocyte carcinoma treatment and at least 1 International Classification of Diseases, Ninth Revision (ICD-9) and/or Tenth Edition (ICD-10) code for a keratinocyte carcinoma diagnosis on the same date—were included. CPTs and ICD-9 or ICD-10 codes needed to be acceptable anatomic pairings indicating the same area of the body.

A total of 792,393 beneficiaries treated for at least 1 keratinocyte carcinoma were included in the analysis, and the mean (SD) age at first diagnosis was 76.6 (8.1) years. About half (51.8%) of the population were women, and 96.7% were White. A total of 2,415,514 procedurally treated keratinocyte carcinomas were included, and 202,812 were excluded due to unacceptable anatomic pairings of CPT and ICD codes. Of the keratinocyte carcinomas included in the analysis, 796,542 (33%) were BCC; 927,984 (38.4%) were SCC; and 690,988 (28.6%) could not be differentiated by subtype.

Overall, the head and/or neck was the most common anatomic location for treated keratinocyte carcinoma, accounting for 53.8% of cases in the study. The second most common location was upper limb (17.8%). Among BCCs, 63.8% were located on the head and/or neck and 14.9% on the trunk. Regarding SCCs, the most common location was the head and/or neck (44.3%), and the second most common was upper limb (26.7%).

Keratinocyte carcinomas were significantly more common in men (57%) compared with women (43%), and the most common location was the head and/or neck for both men and women (58.7% and 47.3%, respectively). In women, the upper and lower limbs were the next most common locations (18.5% and 16.6%, respectively), while the upper limb and trunk followed head and/or neck among men (17.3% and 11.4%, respectively). In line with prior findings, a higher proportion of women vs men had keratinocyte carcinomas diagnosed on lower limbs, and men had higher percentages of keratinocyte carcinomas on the scalp or neck and ears.

When adjusted for race, ethnicity, and region, the odds of a keratinocyte carcinoma being SCC vs BCC was statistically significantly higher with increasing age (OR, 1.03 per 10-year increase; 95% CI, 1.03-1.03) and male sex (OR, 1.06; 95% CI, 1.05-1.06). The odds of a keratinocyte carcinoma being SCC vs BCC was lower on the trunk area vs the head and/or neck (OR, 0.78; 95% CI, 0.78-0.79).

The study was limited by inclusion of only procedurally treated keratinocyte carcinomas, which might lead to bias toward tumors on the head and neck. The analysis also relied on claims data and therefore the accuracy of diagnostic codes, but utilizing both IDC and CPT codes is a validated method that has shown a positive predictive value of 0.95, the authors noted. The cohort also only included fee-for-service beneficiaries, which may limit generalizability.

“Information from this large-scale cohort study on keratinocyte carcinoma anatomic locations in the US is valuable for improved risk factor differentiation and skin cancer surveillance,” the authors concluded. “Further studies detailing the use of keratinocyte carcinoma ICD codes and prevalence of codes not specifying BCC or SCC should be pursued to further characterize the anatomic locations of keratinocyte carcinomas in the US.”

References

1. Navsaria LJ, Li Y, Tripathy S, et al. Anatomic locations of procedurally treated keratinocyte carcinomas in the US Medicare population. JAMA Dermatol. 2023;159(6):643-647. doi:10.1001/jamadermatol.2023.0611

2. Nagarajan P, Asgari MM, Green AC, et al. Keratinocyte carcinomas: current concepts and future research priorities. Clin Cancer Res. 2019;25(8):2379-2391. doi:10.1158/1078-0432.CCR-18-1122