Both Boswellia Serrata & Guggul have been found to interfere with the major CPY 3A4 enzyme (of the P450 family) which is necessary for the metabolism of several chemo drugs.
So taking one of these supplements concurrently with chemo may reduce the chemo effectiveness &/or increase its side effects.
This does not necessarely mean the supplements should be disregarded in all cases but it means care must be taken as to when & how to use them.
http://www.sciencenews.org/articles/20041002/food.asp
http://www.ncbi.nlm.nih.gov/entrez/q...&dopt=Citation