I heard something about large doses of calcium and vitamin d3 could help some cancers?

Adjuncts only: Overdose on this stuff and you're more likely just to give yourself kidney stones. Talk with your oncologist as well before you try anything like this.

Vitamin D And CANCER: Yes there is some evidence that has shown that people with adequate levels of vitamin d have a significantly lower risk of developing cancer it is known to boost the immune system and has been known to have benefitial effect in breast cancer, prostate cancer, colon cancer and others. Research in journal of cell biology in 2008 showed that vit d can return a cancer cell to normal and healthy state.