able for this group of individuals. Because breast cancer is so common in the general population, there is tremendous ongoing research that may be relevant to NASA and that must be monitored to obtain an understanding of the risk due to exposure to ionizing radiation as well as to high-energy particle radiation.
In 1989, Gail and colleagues published the Gail model for estimation of an individual’s risk for the development of breast cancer over time on the basis of age, age at menarche and age at first birth, family history, and breast biopsy results. By using this model, after entry of the risk factor for a given woman, both her 5-year and lifetime probabilities for breast cancer can be calculated (Gail et al., 1989; Benichou et al., 1997). Women who have had thoracic irradiation or a specific family profile indicative of an inherited DNA mutation, however, cannot be appropriately assessed with the Gail model.
The average age of women selected for the space program is 32 (Jennings and Baker, 2000). Given the astronaut training constraints on pregnancy, however, once female astronauts are admitted into the program, they commonly defer childbearing. Therefore, because many female astronauts delay childbirth, they are at increased risk for breast cancer. The increased risk imposed by radiation while in space is unknown, but it may be an additional risk. The probability that breast cancer would develop to the point of clinical significance in a woman while on a long-duration space mission therefore exists. To what extent should preflight risk assessment include laboratory testing of an individual’s nucleic acid composition as well as conventional screening? Should an individual identified to be at increased risk be eliminated from a long-duration space mission beyond Earth orbit or counseled and allowed to make an informed decision? These are questions for NASA to address in its preparation for exploration-class missions.
A similar scenario can be presented for colon cancer in men and women, particularly as the average age of astronauts increases, and will become more common for other disorders as the understanding of the molecular biology of disease continues its present rapid advance.
is critical that the food supply be adequate, safe, and reliable and that it remains so throughout the mission. Inadequate food and water supplies or contamination or loss of the supplies, particularly since much will have to be generated from recycled materials during the mission, will result in termination of the mission or the loss of life.
Additionally, one must consider methods that can be used to ensure the adequacy of caloric intakes to prevent the ongoing loss of body mass. On the basis of current experience (Lane and Schoeller, 2000), a degree of malnutrition is anticipated in nearly all astronauts during space travel without the use of countermeasures and is expected in even 61 to 94 percent of astronauts with the use of countermeasures. Just as the effects of zero gravity or microgravity on the pharmacodynamics and metabolism of pharmaceuticals are unknown (see below), absorption of nutrients may be problematic, lead-