Question: breast cancer and astra zeneca

I am trying to get information on Astra Zeneca and its conncection with breast cancer.

I have read that Astra Zeneca is the chief sponsor of Breat Cancer Awareness Month and that they are a major manufacturer of breast cancer drugs as well as agricultural chemicals that have been linked to breast cancer. I have also heard that A.Z. owns and operates a number of breast cancer treatment centres and that their primary treatment drug, Tamoxifan, has actually been linked to tumpr growth.

Much of what I have read lacked hard facts, so I am looking for reliable sources where I can find answers.