Recipients of a solid organ transplant face up to a sixfold increase in the risk of developing a basal cell carcinoma – a risk that seems to increase as time passes.

A pretransplant history of squamous cell carcinoma (SCC) increased this risk to 55 times that seen in the general population, Dr. Britta Krynitz and her colleagues reported ( Br J Dermatol. 2015. doi: 10.1111/bjd.14153 ).

But even when the pretransplant SCC group was removed from the final analysis, the risk of basal cell carcinoma after transplant was five times that of the general population, “indicating that a pretransplant SCC has limited effect on BCC risk overall and that organ transplantation per se is a strong driver of posttransplant BCC risk,” wrote Dr. Krynitz of Karolinska Institute, Stockholm, and her coauthors.

“Our results strongly suggest tumor promoter effects of the immunosuppressive drugs in the pathogenesis of post-transplantation BCC,” the team said. “We speculate that calcineurin inhibitors and also antiproliferative drugs, often used in combination with corticosteroids, play a role.”

The researchers investigated the incidence of both BCC and SCC in a cohort of 4,023 patients who underwent solid organ transplant from 2004 to 2011. Their median age at the time of transplant was 53 years; most (59%) received a kidney. Other organs transplanted were liver (22%), heart and/or lung (15%), and other organs (4%). The median follow-up time was 3.4 years; the longest follow-up was 5.5 years.

Only 17 of patients had a history of melanoma, and 19 patients a history of SCC – less than 1% for each skin cancer. Seven percent (301) of patients had experienced some form of nonskin cancer.

By the end of follow-up, 341 BCCs had developed among 175 patients – an incidence of 6.7%. About half developed more than one BCC.

The researchers compared these patients to a group of almost 200,000 nontransplant patients who had developed BCC. Among these, the median age at BCC appearance was significantly older (71 years); 39% had more than one lesion.

The overall relative risk of BCC was increased sixfold in transplant recipients and was similar between the genders. However, the risk varied according to the type of organ received. Kidney recipients were at the highest risk (relative risk, 7.2), and those who received other organs had a lower risk (heart/lung: RR, 5.8; liver: RR, 2.6).

The risk also appeared to increase over time, the authors noted. From 0 to 2 years, it was 5.8; from 3 to 5 years, it increased to 7.0.

Among men, 54% of lesions appeared in the head/neck area and 35% on the trunk – a similar distribution to that seen in the nontransplant control group. Among women, there were differences between transplant patients and controls: 44% of lesions appeared on patients’ head/neck, compared with 60% in the control group, and 34% appeared on the truck, compared with 24% in the control group.

Histology was similar, as were the proportions of aggressive type II and highly aggressive type III lesions.

A total of 199 SCCs developed among 87 patients during follow-up, a ratio to BCC of 1:1.7. “The low ratio was probably due to the short follow-up in our study,” the authors noted.

The Welander Foundation, the Westerberg Foundation, and the Strategic Research Program in Epidemiology at Karolinska Institute sponsored the study. None of the authors had any financial declarations.