Risk Factor Number and Recurrence, Metastasis, and Disease-Related Death in Cutaneous Squamous Cell Carcinoma

Importance Cutaneous squamous cell carcinoma (CSCC) risk stratification is central to management, and physicians rely on tumor staging systems to estimate risk. The Brigham and Women’s Hospital (BWH) T staging system predicts risk based on 4 tumor risk factors (RFs). However, stage is not precisely associated with the number of RFs, as BWH stage T2b includes CSCCs with 2 and 3 RFs. Objective To determine how RF number is associated with the risk of recurrence, metastasis, and disease-related death. Design, Setting, and Participants This retrospective multination cohort study of CSCCs diagnosed between October 1, 1991, and July 19, 2023, was conducted at 12 centers in the US (10), Spain (1), and Brazil (1). Invasive CSCCs with confirmed negative margins longer than 14 days were included. Tumors were excluded if they were metastatic at presentation or received adjuvant therapy. Data were analyzed from October 2023 to August 2024. Interventions or Exposures CSCCs were stratified by the number of the following RFs (0, 1, 2, 3, or 4): a diameter of 2 cm or larger, poorly differentiated histology, tumor extension beyond subcutaneous fat, and large caliber nerve invasion. Main Outcomes and Measures Five-year cumulative incidences of local recurrence, nodal metastasis, distant metastasis, and disease-specific death. Results A total of 16 844 CSCCs were included (5978 female individuals [35.5%]; median [IQR] age, 73.9 [65.7-81.8] years), with 0 (12 657 [75.1%]), 1 (2892 [17.2%]), 2 (1015 [6.0%]), 3 ( 225 [1.3%]) or 4 (55 [0.3%]) RFs. Median (IQ) follow up time was 33.6 (14.5-60.3) months. For local recurrence, the risk increased as the number of RF increased from 0 (1.7%; 95% CI, 1.5%-2.0%) to 1 (5.0%; 95% CI, 4.1%-5.9%) to 2 (8.8%; 95% CI, 7.0%-11.0%) to 3 (16.0%; 95% CI, 11.0%-22.0%) to 4 (33.0%; 95% CI, 19.0%-47.0%; P < .001 for between-group differences). This increase was also observed for nodal metastasis (0.6% [95% CI, 0.4%-0.7%] vs 3.6% [95% CI, 2.9%-4.4%] vs 11.0% [95% CI, 9.2%-13.0%] vs 20.0% [95% CI, 15.0%-26.0%] vs 28.0% [95% CI, 15.0%-42.0%], respectively; P < .001), distant metastasis (0.2% [95% CI, 0.1%-0.3%] vs 1.1% [95% CI, 0.7%-1.6%] vs 2.3% [95% CI, 1.4%-3.4%] vs 7.9% [95% CI, 4.6%-12.0%] vs 8.4% [95% CI, 2.6%-19.0%], respectively; P < .001), and disease-specific death (0.3% [95% CI, 0.2%-0.4%] vs 1.9% [95% CI, 1.4%-2.7%] vs 5.4% [95% CI, 4.0%-7.0%] vs 11.0% [95% CI, 6.7%-16.0%] vs 25% [95% CI, 12%-39%], respectively; P < .001). CSCCs with 3 RFs had higher cumulative incidences of local recurrence (1.6-fold), nodal metastasis (1.9-fold), distant metastasis (4.3-fold), and disease-specific death (1.9-fold) compared with those with 2 RFs. Conclusions and Relevance The results of this cohort study suggest that the number of RFs is an indicator of risk, and among BWH T2b tumors, those with 3 RFs represent a higher risk subset.