Does anyone in this day and age still believe that smoking doesn’t cause lung cancer? The epidemiological evidence of the association is bulletproof. However, the majority of smokers don’t get lung cancer. In fact, there are complex statistical models that allow a pretty accurate calculation of risk in populations based on how long and how much a smoker has been smoking. For example, if you start smoking at age 18 and smoke two packs a day, by age 55, you have about a 5% chance of dying of lung cancer and by age 75 you have about a 20% chance of dying of lung cancer. That’s a far lower chance than an HIV-positive patient has of progressing to full-blown AIDS in 10 years (approximately 50%); yet no one seriously disputes that smoking is a very strong risk factor for lung cancer. At the population level, the association is very strong. However, if I see a 65-year-old patient who has been smoking since age 18, I can’t tell him whether he will definitely get lung cancer. I can only quote probabilities. Between two 65-year-olds who are heavy smokers, one may be perfectly fine and another may have stage IV lung cancer.
Let’s look at another example: Breast cancer. Let’s look at stage IV disease, which is, in essence, 100% fatal eventually. However, we do have pretty good estimates of median survival and what a patient’s chance of living 6, 12, 24, and 36 months are. However, when faced with a single breast cancer patient with stage IV disease, we are pretty poor at predicting how long that particular patient will survive. We can’t give a good answer to this poor hypothetical patient’s question, “How long have I got left?” We can only quote probabilities. One woman might deteriorate and die in 6 months, while all of us involved in the care of breast cancer patients have seen the occasional patient who has lived with metastatic disease for several years and done mostly well.
Examples like this abound in the medical literature. The fact that HIV “dissidents” again think this new paper describes some phenomenon unique to HIV again shows their ignorance of the totality of the biomedical literature.