Dr Laking, a cancer specialist, and Dr Reid focus on Herceptin because of its high price and because it is made from living cells. This makes it harder to produce a "bio-similar" copy.
Before the drug had state funding for the treatment of early-stage "Her 2 positive" breast cancer, a one-year course could cost more than $100,000.
Pharmac and district health boards in 2007 funded a nine-week course, saying a full year's therapy was not cost-effective. The incoming National Government overruled that in December 2008 and the funded course was extended to one year.
A bio-similar for Herceptin was approved for use in India last year.
Dr Laking said making bio-similars, or generic drugs, for Herceptin and other "biological" medicines would rely heavily on access to the clinical trial data for the patent drugs.
"Not having to release that information is another way of protecting an intellectual property asset."
He and Dr Reid wrote: "The US is rumoured to have secured agreement to new rules in the TPP on exclusivity over the clinical trial information for at least eight years."
A spokeswoman for Mr Groser said: "The minister has said publicly on numerous occasions that New Zealand will not negotiate on the fundamentals that make Pharmac successful."