McQueen's last two film performances were in the unusual Western Tom Horn (1980), then he portrayed real-life bounty hunter Ralph "Papa' Thorson (Ralph Thorson) in The Hunter (1980). In 1978, McQueen developed a persistent cough that would not go away. He quit smoking cigarettes and underwent antibiotic treatments without improvement. Shortness of breath grew more pronounced and on December 22, 1979, after he completed work on 'The Hunter', a biopsy revealed pleural mesothelioma, a rare lung 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. McQueen later gave a medical interview in which he believed that asbestos used in movie sound stage insulation and race-drivers' protective suits and helmets could have been involved, but he thought it more likely that his illness was a direct result of massive exposure while removing asbestos lagging from pipes aboard a troop ship while in the US Marines.
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 an unconventional treatment after American doctors told him they could do nothing to prolong his life. Controversy arose over McQueen's Mexican trip, because McQueen sought a non-traditional cancer treatment called the Gerson Therapy 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.
McQueen returned to the United States in early October 1980. 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. In late October, McQueen flew to Ciudad Juarez, Chihuahua, Mexico to have an abdominal tumor on his liver (weighing around five pounds) removed, despite warnings from his American doctors that the tumor was inoperable and his heart could not withstand the surgery. McQueen checked into a Juarez clinic under the alias "Sam Shepard" where the local Mexican doctors and staff at the small, low-income clinic were unaware of his actual identity.
Steve McQueen passed away on November 7, 1980, at age 50 after the cancer surgery which was said to be successful. He was cremated and his ashes were scattered at sea. He married three times and had a lifelong love of motor racing, once remarking, "Racing is life. Anything before or after is just waiting.".
He owned a number of classic motorcycles, as well as several exotics and vintage cars, including: Porsche 917, Porsche 908, and Ferrari 512 race cars from Le Mans (1971) Porsche 911S (used in the opening sequence of Le Mans) 1963 Ferrari 250 GT Berlinetta Lusso 1967 Ferrari 275GTB/4 1956 Jaguar XKSS (right-hand drive) (now on exhibit at the Petersen Automotive Museum in Los Angeles, California) 1958 Porsche 356 Speedster 1600 Super (According to his son Chad, this was the first new car McQueen bought. Black exterior, interior and top) (McQueen drove the car in numerous SCCA racing events) 1968 Ford GT40 (Gulf liveried) (used in Le Mans) 1953 Siata 208s (McQueen replaced the Siata badges with Ferrari badges and called it his "little Ferrari") 1967 Mini Cooper-S (McQueen had the car customized by Lee Brown with changes including a single foglight, a wood dash, a recessed antenna and a custom brown paint job) 1951 Chevrolet Styline De Lux Convertible (used in The Hunter (1980), McQueen bought the car in 1979 after filming ended) 1952 Chevrolet 3800 pickup camper conversion (McQueen used the truck for cross-country camping trips. It was the last car he rode in before his death) 1950 Hudson Commodore convertible 1952 Hudson Wasp 2-door sedan 1953 Hudson Hornet 4-door Sedan 1956 GMC Suburban 1958 GMC Pickup Truck (Reportedly one of McQueen's favorite cars, it is powered by a 336 Ci V8 which has been modified. The tag "MQ3188" is a reference to the ID number assigned to him when he was in reform school) 1931 Lincoln Club Sedan 1935 Chrysler Airflow Imperial Sedan 1969 Chevrolet Baja Hickey race truck (Originally debuted at the 1968 Mexican 1000 Rally and was driven by Cliff Coleman, Johnny Diaz, Mickey Thompson and others during its racing career. Said to be the first truck specifically constructed by GM for use in the Mexican 1000, McQueen bought it from General Motors in 1970.).