Much of the excitement at the American Society of Clinical Oncology meeting in Chicago centred around Roche's breast cancer antibody drug conjugate T-DM1, which combines the Swiss major's blockbuster Herceptin with partner ImmunoGen's chemotherapy DM1.

Top-line results of the 991-patient Emilia study were presented in April and the full data highlighted at ASCO showed that T-DM1 (trastuzumab emtansine) was significantly better than the current drug regimen at keeping HER2-positive metastatic breast cancer patients' advanced tumours from progressing. Specifically, the median amount of time people on T-DM1  had no cancer growth was 9.6 months, compared to 6.4 months for people receiving GlaxoSmithKline’s Tykerb/Tyverb (lapatinib) and Roche chemotherapy Xeloda (capecitabine). After two years, 65.4% of the T-DM1 patients were alive, compared to 47.5% of those on the Tykerb/Xeloda combo.

The difference, while a notable trend, failed to meet a statistical benchmark set by its predetermined study design and a later analysis of overall survival is planned. Nevertheless, lead study author Kimberly Blackwell of Duke University noted that "these are significant and clinically meaningful improvements against comparative drugs that are highly effective for this group of patients".

Also, T-DM1 caused fewer side effects. Dr Blackwell noted that while the ADC caused liver injury and a drop in blood platelets in some participants, most did not suffer the hair loss, rashes, nausea and diarrhoea common to traditional chemotherapies. As a result, more people were able to stay on the drug without dose reductions, with 16.3% of participants on T-DM1 needing to adjust the dosage, compared to 53.4% on Xeloda and 27.3% for Tykerb.

"This is a more targeted way of delivering chemotherapy to HER-2 overexpressed cells," Dr Blackwell said. "It delivers the drug directly to the cancer cells, while avoiding cells that don't really need to receive chemotherapy, which keeps patients from getting sick."

She went on to say that "this drug has very little dose-limiting toxicity", which is in "stark contrast to so many of the treatments we have available today. This drug works."

Roche will file T-DM1 with regulators in the USA and Europe based on the Emilia study. In August 2010, the US Food and Drug Administration rejected a request for accelerated approval of T-DM1, saying that patients in the study population had not exhausted all available treatment options.

Kevin Grogan in Chicago