Background Keratinocyte cancers (KC) are common and pose a significant financial burden globally. Ultraviolet radiation is a significant factor in their development, through mutagenesis promotion but also through local and systemic immunosuppression. Although systemic immunosuppression is well understood, cutaneous immunity has been more difficult to evaluate.

Objectives This study used a contact sensitizer, diphencyprone (DPCP), which elicits a contact hypersensitivity reaction in skin, to compare the degree of reactivity to DPCP in patients with a high KC burden versus those with a low KC burden.

Methods A prospective study was performed in immunocompetent patients aged 70 ± 5 years of age, comparing patients with a high KC burden (>10 previous KC) with those with a low KC burden (<2 previous KC). All patients were sensitized with 2% DPCP and then patch tested two weeks later with eight different concentrations of DPCP with the threshold concentration and total degree of reaction recorded.

Results Nine patients were recruited, 5 in the ‘high cancer’ group and 4 in the ‘low cancer’ group. All patients were Fitzpatrick skin type 1 or 2. All patients developed a reaction to DPCP. Patients in the low cancer group developed a reaction at a significantly lower threshold DPCP concentration than the high cancer group (P = 0.039). The cumulative intensity of reaction was higher in the low cancer group (P = 0.087).