An NIH study published in March of 2023 showed that Ashwagandha can be used to treat breast, prostate, lung, colon, melanoma,and blood cancers using the roots, stems and leaves.  

It not only can be used as a supportive herb during cancer treatments like radiation but kills cancer cells and heals internal organs that are damaged by radiation therapy. It has been proven effective against melanoma. It kills the melanoma, stops it from spreading and stops the reproduction of the cancer cells. It also acts like a chemotherapeutic agent against several different breast cancer types, along with actually preventing several types of breast cancers.

They showed that Ashwagandha improves the overall health of patients suffering with breast cancer. Intermittent fasting and an extract showed results in certain breast cancers and more importantly a very serious but most common form of brain cancer. It either starts in the brain or the spinal cord.

2000mg daily was used for repair of chemotherapy treatments. If using for cancer treatment itself I would start with  1000 mg and work your way up to  2000mg.