Perejta, the first breast cancer drug to be used pre-surgery, received approval from the U.S. Food and Drug Administration (FDA) on Monday for use in preventing a specific form of the cancer from quickly spreading to other parts of the body.

The Roche-produced biotech drug isn’t intended for use in all breast cancer patients, however, only those who carry tumors that over-produce a protein known as HER-2, which appears in roughly 20 percent of all patients. Perejta was originally approved as a post-surgery treatment, but cancer specialists now see the potential for reducing tumor growth pre-surgery as a means to avoid mastectomies — full breast removal — eventually down the line.

"By making effective therapies available to high-risk patients in the earliest disease setting, we may delay or prevent cancer recurrences," FDA's Dr. Richard Pazdur, who directs the agency's office of cancer products, told the Associated Press.

Surgery is typically the first line of defense in removing tumors. Doctors hope Perejta’s added effectiveness in shrinking tumors will allow for fewer, less-invasive measures. Doctors also speculate that the treatment could prevent tumor recurrence later in life, although clinical trials haven’t proven these hunches. Chemotherapy drugs have been widely used in treating cancer pre-surgery despite no FDA approval.

Monday’s approval came after a 417-person, long-term study found Perejta as the most effective in comparisons with older breast cancer treatments. Women who had taken Perejta were more likely to be cancer-free after the 12-week study period than users of other drugs. Perejta received accelerated approval when combined with another Genentech drug, Herceptin. Accelerated approval means it displayed groundbreaking results in terms of its efficacy for treating life-threatening diseases in early studies.

Overall approval remains contingent on a larger follow-up study, which is expected to take place in 2016 and include 4,800 patients. Despite the follow-up study’s distant timeline, some cancer specialists have already said they’ll start administering the drug to early-stage patients.

"This does not yet prove to us that using the antibody in this setting will result in more cures,” says Dr. Paula Klein, who heads the breast cancer program at Continuum Cancer Centers of New York. “That is still a hypothesis.”

A spokeswoman for Genentech said a regimen of Perjeta plus Herceptin would cost between $27,000 and $49,000, depending on how long the patient takes the combination, the AP reports. Perjeta’s label will recommend a course of treatment between nine and 18 weeks.

Breast cancer kills nearly 40,000 Americans each year, according to the National Cancer Institute. About 6,000 to 8,000 deaths per year are attributed to the HER-2 form of the disease. When detected early, breast cancer is highly treatable: roughly 98 percent of women diagnosed in the first stage go on to live at least the next five years.