Premalignant lesions, basal cell carcinoma and melanoma in patients with cutaneous squamous cell carcinoma.

The incidence of keratinocyte carcinomas is increasing worldwide and currently there is no standardised strategy for the follow-up of patients with multiple tumours. The objective of this study was to assess the prevalence of premalignant lesions, i.e., actinic keratosis and Bowen's disease, as well as basal cell carcinoma (BCC) and cutaneous melanoma (CM) among patients with cutaneous squamous cell carcinoma (cSCC). Pathology database search was performed to identify all cSCC patients diagnosed in the Pirkanmaa region of Finland in 2006-2015. Details of the patients and tumours were obtained through medical record review. The cohort consisted of 774 patients with 1131 cSCC tumours. Overall 559 patients (72%) had premalignant lesions. A total of 316 patients (41%) had BCC and 52% of these (n = 164) had more than one BCC tumour. 50 patients (6%) had CM. Overall 180 cSCC patients (23%) had no premalignant changes, BCC or CM. The median age of these patients was 6 years less than that of the patients with premalignant lesions (p < 0.001) or BCC (p < 0.001). The invasion depth of the tumours was deeper in the patients with only cSCC (median 3 mm, interquartile range 2-6) than in those with premalignant lesions or BCC (median 2 mm, interquartile range 1-3), p < 0.001. CSCC patients have a high risk of developing multiple skin cancers and need long-term follow-up.