Ratio of Nonmelanoma Skin Cancer Histologic Subtypes in a South Florida Dermatology Practice: High Incidence of Squamous Cell Carcinoma Subtypes

Background: Ultraviolet Radiation (UVR), both UVA and UVB, are established causes of nonmelanoma skin cancers (NMSC); primarily basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) subtypes. Because of its demographics and geographic location, the population of Florida is at risk for some of the highest rates of NMSC in the world. While current dermatologic epidemiology states that over 70% of NMSC are BCC, a previous 2012 study in South Florida showed a much higher incidence of SCC subtypes. Methods: The electronic histopathology database associated with a clinical dermatology practice in South Florida was searched for all histologically-confirmed NMSC results across all ages for the full year of 2024. Results: A total of 856 lesions with biopsy-proven NMSCs were assessed and categorized into BCC and SCC subgroups. BCC subgroups included superficial, nodular, morpheaform, and other subtypes. SCC subgroups included in situ SCC (isSCC) and all invasive SCC subtypes, including SCC and keratoacanthoma type. Among these lesions, 247 (28.9%) were BCC subtypes and 609 (71.1%) were SCC subtypes. Further categorized, 54 were superficial BCC (6.24%), 193 were BCC (22.31%), 268 were isSCC (30.98%), and 341 were SCC (39.42%). Discussion: The 2024 incidence rates reveal very high ratios of SCC versus BCC. Our findings are in line with the findings from the previous study from South Florida, which may challenge the historical ratio of BCC to SCC. In this study, SCC subtypes including isSCC represented over 70% of all biopsy-confirmed NMSC. We hypothesize this trend may be attributed to different factors. First, the historical use of UVB-specific over more modern broad-spectrum sunscreens allowed for much greater UVA exposure without UVB burns may account for the higher rates of SCC. Indeed, the ratio of this patient cohort more closely mimics long term PUVA or organ transplant populations. Since many SCC subtypes may arise from Actinic Keratoses (AK) current dermatologists may be misdiagnosing early SCC including isSCC as AK and directly destroying the lesions with liquid nitrogen instead of taking a biopsy to determine if they are SCC. Additionally, this study highlights the importance of treating AK to prevent future SCC. Conclusion: Our patient population showed a significantly higher incidence of SCC than BCC within NMSC, which contradicts current teachings. Further study is warranted.