"Dressed to Kill" and Breast Cancer

The book "Dressed to Kill" was published in 2005 and I was not aware of it till a few days ago. I haven't read it but read some comments and related articles about the same topic, relationship between breast cancer and wearing bras. There're a couple of comments I want to make. Briefly,

1. The relationship is unproven according to American Cancer Society's research (also this). Then how is any study scientific? One of the most compelling review of Sydney Ross Singer et al.'s book is by D. Pilipovich (Kapaau, HI United States). There may be some medical hypotheses that can't be or can't easily be studied by single- or double-blind methods. If ACS does not think this is one of them, then there should be a panel of experts that organize such a study. Singer's study may be too simplistic, not excluding too many confounding factors. But if the cohort number is large enough, it doesn't really matter, although the explanation for the observed relationship may be questionable. This reminds me of some ever-lasting debate in relational databases, such as Oracle. Should one rebuild a table's index or not? In spite of experts' caution, if you rebuild it and it improves performance and it doesn't realistically cause downtime or problem either now or in the near future, do it. By the same token, if a survey of a large number of respondents corroborates the "rumor", give the rumor credit. Even though the theory behind the rumor given by the researchers (Singer and Grismaijer here) is not sufficiently substantiated, the survey result is hard fact and cannot be dismissed unless you find flaws in the survey itself. (I haven't read the book. The theory of lymphatic flow restriction sounds plausible but I wonder why they pick the lymphatic, not for instance blood flow.)

2. Chinese women living in cities generally wear tighter clothing, and possibly tighter bras, and yet have less common occurrences of breast cancer than American women. Do eating more tofu, more exercise (walking and biking) and possibly less smoking explain the difference?

Other articles supporting Singer et al.'s claim:
Bras And Breast Cancer
Health After 40
Bras and Breast Cancer