Research oncologists are not given to hyperbole, so when the words, “extraordinary” and “unprecedented” are used during a scientific presentation you need to pay attention.

At the recently-concluded European Society of Medical Oncology meeting in Madrid, this is exactly how the results for the CLEOPATRA breast cancer study on Roche’s Perjeta (pertuzumab) were described.

“Many of us work our whole career to have this kind of data,” said Sandra Swain, medical director of the Washington Cancer Institute, and lead investigator of the CLEOPATRA study. “I’ve been doing this for about 30 years and I have to say, this is very exciting for me, and the patients I treat.”

The purpose of CLEOPATRA was to look at combining one of the most successful cancer drugs ever created, Roche’s HER2 receptor-targeting antibody Herceptin (trastuzumab), with Perjeta in a population of HER2-positive, metastatic breast cancer patients.

“Pertuzumab binds at a different site on the HER2 receptor than trastuzumab,” said Dr Swain at a press conference discussion on CLEOPATRA. “And both the preclinical, and then early clinical data supported the idea of using the two together rather than sequentially.”

Over 800 patients at 204 medical centres in 25 countries participated in CLEOPATRA. Patients were randomized in a blinded fashion to treatment with either pertuzumab plus trastuzumab and docetaxel, or the same regimen with placebo replacing the pertuzumab.

Patients remained on therapy until their disease progressed and after a median follow up of 50 months, data for overall survival were analyzsed.

As reported by Dr Swain, these analyses showed an improvement of 15.7 months in survival for the monoclonal combination as compared to using just trastuzumab alone.

“The median survival for trastuzumab is already very good at 40.8 months, and that alone really changed things for patients for HER2-positive breast cancer,” said Dr. Swain. “Adding pertuzumab increased it by 15.7 months – so to me that’s incredible. I’ve never seen that in any other trial in metastatic breast cancer.”

The improvement in survival did come with an elevated rate of adverse events for the combination; a greater incidence of rash, mucositus, and diarrhea were observed. However, there was no increase in events related to cardiotoxicity - though these events had been anticipated due to prior adverse events observed with trastuzumab, and the similar mechanism of action for pertuzumab.

After the reporting of the CLEOPATRA results, the response from other clinicians was immediate, and striking. Luca Gianni, of the San Raffaele Scientific Institute in Milan, Italy stated: “The combination of docetaxel/trastuzumab/pertuzumab is the new standard – not an option – for first line treatment of HER2-positive metastatic breast cancer.”