Medicinal cannabis is under clinical trial. But not for a cure for breast cancer but to relieve nausea and pain for palliative patients . I expect the lady you were speaking with was also on other medication that were prescribed to reduce tumours as they keep trying different medications until one works. Do remember that most drugs were sourced originally from nature itself. Getting consistent doses etc is how medication was created. Even chemo comes from nature itself.
Anyway here is the link to clinical trials.
https://www.medicinalcannabis.nsw.gov.au/clinical-trials