Another class of medications potentially associated with increased development of nonmelanoma skin cancer (NMSC) is the JAK inhibitors (also known as jakinibs). Many proinflammatory signaling pathways converge on the JAK family of enzymes—JAK1, JAK2, JAK3, and TYK2. These enzymes operate in cytokine signal transduction by phosphorylating activated cytokine receptors, which allows for recruitment and activation by means of phosphorylation of transcription factors collectively known as signal transducers and activators of transcription (STATs). Phosphorylated STATs dimerize and translocate to the nucleus, acting as direct transcription promoters. Janus kinase inhibitors modulate the immune response by reducing the effect of interleukin and interferon signaling.
Ruxolitinib, a JAK1/JAK2 inhibitor, was the first JAK inhibitor approved by the FDA and is indicated for the treatment of myelofibrosis and polycythemia vera. Additionally, oral and topical JAK inhibitors have shown efficacy in the treatment of psoriasis, rheumatoid arthritis, alopecia areata, vitiligo, and pruritus from atopic dermatitis.28
The JAK-STAT pathway is complex, and the biological activity of the pathway is both proinflammatory and pro–cell survival and proliferation. Because signaling through the pathway can increase angiogenesis and inhibit apoptosis, inhibition of this pathway has been exploited for the treatment of some tumors. However, inhibition of interferon and proinflammatory interleukin signaling also can potentially promote tumor growth by means of inhibition of downstream cytotoxic T-cell signaling, theoretically increasing the risk for NMSC. A study examining the 5-year efficacy of ruxolitinib in myelofibrosis patients (COMFORT-II trial) found that 17.1% of patients developed NMSC compared to only 2.7% of those on the best available therapy. After adjustment by patient exposure, the NMSC rate was still doubled for ruxolitinib-treated patients compared to controls (6.1/100 patient-years and 3.0/100 patient-years, respectively).29 Eighty-week follow-up of the phase 3 clinical trial of ruxolitinib for the treatment of polycythemia vera also noted an increased incidence of NMSC, albeit a more conservative increase. Patients randomized to the ruxolitinib treatment group developed NMSC at a rate of 4.4/100 patient-years, whereas the rate for controls treated with best available therapy was 2.7/100 patient-years.30 In contrast, 5-year follow-up of the COMFORT-I trial, also examining the efficacy of ruxolitinib in myelofibrosis, showed no increased risk for NMSC between ruxolitinib-treated patients and placebo (2.7/100 patient-years and 3.9/100 patient-years, respectively).31
A 2017 case series described 5 patients with myelofibrosis who developed multiple skin cancers with aggressive features while receiving ruxolitinib.32 Duration of ruxolitinib therapy ranged from 4 months to 4 years; 3 patients had a history of hydroxyurea exposure, and only 1 patient had a history of NMSC. High-risk cutaneous SCC, undifferentiated pleomorphic sarcoma, and lentigo maligna melanoma (Breslow thickness, 0.45 mm) were among the tumors reported in this series. Although no definitive conclusion can be made regarding the causality of JAK inhibitors in promoting these tumors, the association warrants further investigation. Clinicians should be aware that ruxolitinib might amplify the risk for NMSC in patients with pre-existing genetic or exposure-related susceptibility. Interruption of drug therapy may be necessary in managing patients who develop an aggressive tumor.32
In contrast, tofacitinib, which specifically inhibits JAK3, carries very low risk, if any, for NMSC when used for the treatment of psoriasis and rheumatoid arthritis. Results from 2 phase 3 trials analyzing the efficacy of tofacitinib in psoriasis demonstrated that only 2 of 1486 patients treated developed NMSC compared to none in the control group.33 Furthermore, analysis of NMSC across the tofacitinib rheumatoid arthritis clinical program, which included a total of 15,103 patient-years of exposure, demonstrated that the overall NMSC incidence was 0.55 for every 100 patient-years. Of note, the risk in patients receiving high-dose treatment (10 mg vs 5 mg) was nearly doubled in long-term follow-up studies (0.79/100 patient-years and 0.41/100 patient-years, respectively). Overall, the study concluded that treatment with tofacitinib presents no greater increased risk for NMSC than treatment with tumor necrosis factor inhibitors.33
Phosphodiesterase 5 inhibitors, such as sildenafil citrate, have been widely prescribed for the treatment of erectile dysfunction. Studies have shown that BRAF-activated melanomas, which occur in approximately 50% to 70% of melanomas, also result in reduced PDE-5 expression.34-36 In these melanomas, downregulation of PDE-5 results in increased intracellular calcium,36 which has been shown to induce melanoma invasion.36,37 Given this similarity in molecular pathway between BRAF-activated melanomas and PDE-5 inhibitors, there has been increased concern that PDE-5 inhibitors might be associated with an increased risk for melanoma.
In 2014, Li et al38 published a retrospective analysis suggesting an association with sildenafil and an increased risk for melanoma. Their study utilized the Health Professionals Follow-up Study to identify a statistically significant elevation in the risk for invasive melanoma with both recent sildenafil use (multivariate-adjusted HR=2.24) and use at any time (HR=1.92). These results controlled for confounding variables, such as presence of major chronic disease, use of other erectile dysfunction treatments, family history of melanoma, history of sun exposure, and UV index of the patient’s residence. Notably, the study also found that sildenafil did not affect the incidence of BCC or SCC.38