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McQueen developed a persistent cough in 1978. He gave up cigarettes and underwent antibiotic treatments without improvement. Shortness of breath grew more pronounced and on December 22, 1979, after filming The Hunter, a biopsy revealed pleural mesothelioma,[63] a cancer associated with asbestos exposure for which there is no known cure. The asbestos was thought to have been in the protective suits worn in his race car driving days, but in fact the auto racing suits McQueen wore were made of Nomex, a DuPont fire-resistant aramid fiber that contains no asbestos. By February 1980, there was evidence of widespread metastasis. While he tried to keep the condition a secret, the National Enquirer disclosed that he had "terminal cancer" on March 11, 1980. In July, McQueen traveled to Rosarito Beach, Mexico for unconventional treatment after US doctors told him they could do nothing to prolong his life.[64]
Controversy arose over McQueen's Mexican trip, because McQueen sought a non-traditional cancer treatment that used coffee enemas, frequent washing with shampoos, daily injections of fluid containing live cells from cows and sheep, massage and laetrile, a supposedly "natural" anti-cancer drug available in Mexico, but not approved by the US Food and Drug Administration. McQueen paid for these unconventional medical treatments by himself in cash payments which was said to have cost an upwards of $40,000 per month during his three-month stay in Mexico. McQueen was treated by William Donald Kelley, whose only medical license had been (until revoked in 1976) for orthodontics.[65] Kelley's methods created a sensation in the traditional and tabloid press when it was known that McQueen was a patient.[66][67] McQueen returned to the US in early October. Despite metastasis of the cancer through McQueen's body, Kelley publicly announced that McQueen would be completely cured and return to normal life. McQueen's condition soon worsened and "huge" tumors developed in his abdomen.[65] In late October 1980, McQueen flew to Ciudad Juárez, Chihuahua, Mexico to have an abdominal tumor on his liver (weighing around five pounds) removed, despite warnings from his US doctors that the tumor was inoperable and his heart could not withstand the surgery.[65][68] McQueen checked into a Juarez clinic under the assumed name of "Sam Shepard" where the doctors and staff at the small, low-income clinic were unaware of his actual identity. On November 7, 1980, Steve McQueen died at the age of 50 at the Juárez clinic following the surgical operation to remove or reduce several metastatic tumors in his neck and abdomen.[68] He had in fact died of cardiac arrest at 3:45 am in his hospital bed more than 12 hours after the surgery to remove the tumors. An article in the El Paso Times noted that before his death he awoke in his hospital bed and asked the nurse for some ice water and then died.
A few months before his death, McQueen had given a medical interview in which he blamed his condition on asbestos exposure.[69] While McQueen felt asbestos used in movie sound stage insulation and race-drivers' protective suits and helmets could have been involved, he believed his illness was a direct result of massive exposure while removing asbestos lagging from pipes aboard a troop ship while in the Marines