More than three-quarters of breast cancers are hormone-sensitive, and endocrine therapy - a hormone treatment - is a recommended to prevent cancers from growing.
It does so by stopping women from producing oestrogen, or stopping their oestrogen from acting on cells.
The treatment leaves women oestrogen deficient and side effects experienced by about 70 per cent of women can significantly disrupt their lives, Monash University Professor Susan Davis said.
"These are symptoms where women have to stop what they're doing ... (and) that will wake women two or three times at night, often with drenching sweats," Prof Davis told AAP.
"Most women will say, 'I can cope with it during the day, but if I can't sleep and I'm just constantly walking around like a zombie, I can't cope.'"
A staggering number of women end up stopping their endocrine therapy because of side effects, Prof Davis suggests, with estimated figures sitting about 30 per cent.
For many, it's a decision between quality of life and the length of their life, or the risk of breast cancer returning.
"They will not necessarily go on to alternative therapies to treat their breast cancer - they just stop their breast cancer therapy," Prof Davis said.
"The main reason people are on these treatments is to block the return of cancer."
A Monash University-led trial involving about 130 women has shown a new drug, called "Q-122", can significantly reduce the side effects of endocrine therapy.
The number and severity of women's hot flushes and night sweats was reduced because of the drug.
They also slept better, and the treatment had no serious adverse affects.
The findings of the trial, conducted with medical research company QUE Oncology, represent a quantum leap forward for women with breast cancer, Prof Davis said.
Researchers are yet to determine exactly how the Q-122 drug works but they know it interacts with a part of the brain that controls body temperature regulation.
They anticipate the drug could also be used for postmenopausal women who experience hot flushes and night sweats, and who need an alternative to oestrogen therapy to treat their symptoms.
"There are some other medical conditions where we perhaps would not want women to take oestrogen - say, if they've had a heart attack or stroke" Prof Davis said.
"This offers a potential alternative for the broader community, not just for women after breast cancer."
The research was published in medical journal The Lancet on Friday.
