Preclinical and phase 1 clinical trials in various cancers have shown that curcumin (isolated from turmeric) may be useful in the chemoprevention of colon cancer in humans (Azuine & Bhide, 1994).
It has further been shown that curcumin inhibits proliferation and helps kill cancer cells. These are attributed to the ability of this molecule to positively interfere in the functioning of cancer-causing genes (Bar-Sela & Schaffer, 2011).
Ar turmerone isolated from turmeric is said to suppress the growth of leukemia cells (Kuo et al., 1996).
The anticancer action of curcumin is attributed to its ability to inhibit a cancer master switch, which is called nuclear factor kappa beta. Inflammation is said to fuel the nuclear factor kappa beta activity, which is claimed to account for 95% of all cancers. Cancer activity is also indicated by high interleukin 6 (IL6) levels in the blood.
Stage 2 and, in some cases, stage 3 clinical trials are underway to validate turmeric’s anti-inflammatory, anticancer, and anti-Alzheimer properties (Cole et al., 2007).
Turmeric is emerging as a possible option for the treatment of cancer.
I did not find any scientific evidence supporting the anticancer properties of Azadirachta indica (common name neem). It is also not listed as an anticancer herb in Ayurvedic formulations.