In 1971, he reported in the "New England Journal of Medicine" that solid tumors are angiogenesis-dependent. He hypothesized that there was an unknown "factor" that tumors secreted to help it increase its blood supply, and that if that factor could be blocked, tumors would wither and die. Though his hypothesis was initially disregarded and treated with skepticism by most experts in the field, Folkman persisted with his research. He and collaborators, who included Bert L. Vallee, soon identified the already-known fibroblast growth factor as an angiogenic factor, but the team's work showed that there were additional, unknown factors. To help accelerate the work, Folkman started collaborating with industry. In 1974 Harvard University and Monsanto signed a ten-year industrial-funded research grant to support his cancer research, which at that time was the largest such arrangement ever made; medical inventions arising from that research were the first for which Harvard allowed its faculty to submit a patent application. Robert Langer worked as a postdoc in Folkman's lab during this time, concentrating on using silastic and other materials to deliver drugs.