Since August 2009, the U.S. FDA has required warnings to be placed on packaging with respect to increased risks of certain cancers.The risks involved seem to be related both to the duration and the dosage used. People who have previously been treated with an alkylating agent may have an excessive risk of cancers if treated with azathioprine. Epidemiological studies by International Agency for Research on Cancer have provided "sufficient" evidence of azathioprine carcinogenicity in humans (group 1), although the methodology of past studies and the possible underlying mechanisms are questioned.The various diseases requiring transplantation may in themselves increase the risks of non-Hodgkin lymphoma, squamous cell carcinomas of the skin, hepatobiliary carcinomas, and mesenchymal tumours to which azathioprine may add additional risks. Those receiving azathioprine for rheumatoid arthritis may have a lower risk than those undergoing transplantation.Cases of hepatosplenic T-cell lymphoma – a rare type of lymphoma – have been reported in patients treated with azathioprine. The majority occurred in patients with inflammatory bowel disease. Adolescents and young adult males were the majority of cases. They presented with a very aggressive disease course, and with one exception, died of the lymphoma. The FDA has required changes to the labeling to inform users and clinicians of the issue. Skin cancers
In transplant patients, skin cancer is 50 to 250 times more common than in the general population, and between 60 and 90% of patients are affected 20 years after transplantation.
The suggested rate of ascent is the same that applies to the prevention of acute mountain sickness and high-altitude cerebral edema. The Wilderness Medical Society (WMS) recommends that, above 3,000 metres (9,800 ft), climbers

not increase the sleeping elevation by more than 500 metres (1,600 ft) a day, and
include a rest day every 3–4 days (i.e., no additional ascent).In the event that adherence to these recommendations is limited by terrain or logistical factors, the WMS recommends rest days either before or after days with large gains. Overall, WMS recommends that the average ascent rate of the entire trip be less than 500 metres (1,600 ft) per day.The most studied and preferred medication for prevention of HAPE is nifedipine, a pulmonary vasodilator which prevents the altitude induced pulmonary hypertension. The recommendation for its use is strongest for individuals with a history of HAPE. According to published data, treatment is most effective if given one day prior to ascent and continued for four to five days, or until descent below 2,500 meters (8,200 ft).Additional medications that are being considered for prevention but require further research to determine efficacy and treatment guidelines include acetazolamide, salmeterol, tadalafil (and other PDE5 inhibitors), and dexamethasone. Acetazolamide has proven to be clinically effective, but formal studies are lacking. Salmeterol is considered an adjunctive therapy to nifedipine, though only in highly susceptible climbers with clearly demonstrated recurrence of HAPE. Tadalafil was found to be effective at preventing HAPE in HAPE-s individuals during rapid ascent, but optimal dosing and frequency has yet to be established.