Reproductive factors and gall-bladder cancer, and the effect of common genetic variants on these associations: a case–control study in India by Mhatre, S, Lacey, B, Sherliker, P, Chatterjee, N, Rajaraman, P, Goel, M, Patkar, S, Ostwal, V, Patil, P, Shrikhande, SV, Chitkara, G, Badwe, R, Lewington, S, Dikshit, R