High carbohydrate 19-9 antigen serum levels in patients with nonmelanoma skin cancer and primary occult cancer

Background: Non-melanoma skin cancers (NMSC), despite having a favourable prognosis, present an increased risk of occult malignancies. The aim of this study was the evaluation of the usefulness of the mucinous marker carbohydrate 19-9 antigen (CA 19-9) in the diagnosis of occult cancers. (1) Patients and Methods: This is a case control study in which 480 patients with NMSC and 480 matched control subjects with dermatitis were enrolled; 208 patients with NMSC showed upper-normal CA 19-9 values, and 272 showed under-normal CA 19-9 values. (2) Results: The 208 patients positive for CA 19-9 included 87 with basal cell carcinoma (BCC) and 121 with squamous cell carcinoma (SCC). The 272 patients negative for CA 19-9 included 107 with BCC and 165 with SCC. For the SCC patients, CA 19-9 serum levels were significant in 121 of the patients (positive), 66 of which were affected by cancer; CA 19-9 was within the normal range in 165 patients, of which 30 were diagnosed with cancer. In the SCC patients, the CA 19-9 sensitivity was 68%, the specificity was 70%, the positive predictive value (PPV) was 54% (95%) and the negative predictive value (NPV) was 81%. In the BCC patients, the CA 19-9 sensitivity was 70%, the specificity was 66%, the PPV was 48% and the NPV was 83%. In the dermatitis patients (controls), we observed 121 patients that were CA 19-9 positive, with 15 malignancies, and 359 CA 19-9-negative patients, with three malignancies. (3) Conclusions: To confirm the association between CA 19-9 and an elevated risk of malignancies in NMSC, prospective cohort studies should be performed.