For the most part, Calcium-D-Glucarate is just known to be a β-glucuronidase inhibitor via its metabolite D-glucaro-1,4-lactone. The process of 'glucuronidation' is a detoxification process where a group (known as a glucuronide) is attached to a hydrophobic molecule to make it more water soluble, and then the kidneys can better facilitate its removal from the body. This process is positively mediated by the glucuronosyltransferase enzyme, and negatively mediated by the β-glucuronidase enzyme; as such, inhibiting the negative regulator (the enzyme that removes the glucuronide) indirectly increases the activity of this pathway.
It is touted to be an anticancer agent, which is due to a series of past research done in rats and mice exposed to the DMBA toxin which is known to be glucuronidated. There are definitely anticancer effects in these models, and it appears to extend to other toxins that are glucuronidated.
However, a problem occurs when humans take this as an oral supplement. Although it appears to be safe even at high doses, very high doses are required for its effects (100mg/kg minimum, near maximal effects at 200mg/kg) and this would even only theoretically assure some protection against toxins that are glucuronidated. If a toxin can't be glucuronidated and requires another detoxification pathway, it will serve no benefit.
Organ cancer production which just occurs spontaneously because of oxidative stress to DNA is also not likely to be protected against, as increasing glucuronidation does not per se decrease oxidative stress in the body (it might just reduce the oxidative effects of toxins).
Furthermore, all steroid hormones in the body (testosterone, estrogen, DHEA, etc.) are also glucuronidated. If using an oral dose that reduces the toxin, these hormones will also all be reduced for a short time.
Using calcium-D-glucarate as a daily preventative supplement does not appear to be a prudent idea, due to its lack of reliability even in theory and high doses used. However, a single acute dose of this supplement prior to known exposure to toxins that are glucuronidated (such as both benzopyrene and polyaromatic hydrocarbon compounds produced in the cooking of meat products) might be more prudent and potentially useful.