Melanoma only accounts for 2% of all skin cancer cases in the US but causes the majority of skin cancer deaths.
The study authors - including Hilary A. Robbins from the John Hopkins University Bloomberg School of Medicine in Baltimore, MD - suggest the findings may be down to the immunosuppressive drugs transplant recipients need to take in order to prevent rejection of the new organs.
Their results are published in the Journal of Investigative Dermatology.
While melanoma only accounts for 2% of all skin cancer cases in the US, it causes the majority of skin cancer deaths. This year, it is estimated that 73,870 new cases of melanoma will be diagnosed in the US, and almost 10,000 people will die from the cancer.
Robbins notes that previous research had indicated that organ transplant recipients were more likely to develop melanoma, but this had been attributed to more intensive screening; such patients are at greater risk of developing less deadly forms of skin cancer and may have regular dermatologist check-ups as a result.
However, this latest study unveiled a surprising finding: organ transplant recipients were more likely to be diagnosed with melanoma in later stages.
"Since melanoma is not known to be caused by a virus, some thought that melanoma was increased in transplant recipients because of more intensive screening," Robbins told Medical News Today. "Our findings contradict this notion because we found the strongest increase in risk not for localized melanomas - which are likely to be detected during screening - but instead for regional-stage melanomas which have already begun to spread."
Transplant recipients twice as likely to develop melanoma
To reach their findings, the team analyzed the data of 139,991 non-Hispanic white organ transplant recipients who were part of the Transplant Cancer Match Study - a study that holds information on nearly half the transplant population in the US from 1987-2010.
The researchers identified 519 cases of melanoma among these participants and assessed their risk factors for the disease. Melanoma incidence among organ transplant recipients was compared with that of the general population.
From this, the team calculated that organ transplant recipients are twice as likely to develop melanoma than individuals who do not undergo organ transplantation.
- Rates of melanoma in the US have been rising for the past 30 years
- White Americans are around 20 times more likely to develop melanoma than African-Americans
- While the average age of melanoma diagnosis is 62, it is one of the most common cancers in young adults - particularly young women.
Next, the team used a different dataset - including 182 organ transplant recipients with melanoma and 130,000 non-transplant recipients with the disease - to compare patient outcomes over an average of 15 years.
The analysis revealed that 12% of the non-transplant recipients died from melanoma, compared with 27% of the transplant recipients.
The researchers calculated that melanoma patients who had undergone organ transplantation were at three times greater risk of death than non-transplant recipients, regardless of the stage melanoma was diagnosed at.
Organ transplant recipients were also around four times more likely to be diagnosed with stage 2 or 3 melanoma - known as "regional spread" melanoma, where the cancer has spread in the area it began but has not yet spread to other areas of the body. This mostly occurred within the first 4 years after transplantation.
Later-stage melanoma diagnoses among organ transplant recipients were linked with use of an immunosuppressive drug that halts the functioning of T cells - a type of immune cell - and stops them from attacking the new organs, according to the findings.
Early-stage melanoma diagnoses among transplant recipients, however, were more likely among those who received an immunosuppressive drug called azathioprine, which is known to make the skin more sensitive to ultraviolet (UV) radiation - a key risk factor for melanoma.
Immunosuppression causes melanoma to become more aggressive
While it is possible that melanomas among transplant recipients may have started developing prior to transplantation, the team says their findings indicate immunosuppressive medication encourages the cancer to spread.
Robbins told MNT:
"Combined with the observation that melanoma patients who had received a transplant have an increased risk of dying from their melanoma, our results imply that melanoma is not only more common but behaves more aggressively in the setting of transplant-related immunosuppression."
As such, they call for intensive melanoma screening for patients prior to undergoing organ transplantation, as well as careful monitoring following transplantation.
"Closer dermatologic monitoring of transplant recipients, particularly within the first 4 years after transplantation, could enable earlier detection of melanoma and help prevent patients from developing metastatic disease," Robbins told MNT. "Transplant candidates should also be carefully evaluated prior to transplantation, with the goal of removing melanomas that could quickly metastasize in the setting of immunosuppression."
In addition, the researchers say sun safety practices - such as the use of sunscreen and protective clothing - are particularly important for this population.
Last month, MNT reported on a study in which researchers identified a new gene mutation that plays a key role melanoma development.