Herceptin effectiveness undermined

19 May 2008

Class leading breast cancer drug may be less effective than claimed

Researchers writing in The Lancet claim unpublished data from trials of the breast cancer drug Herceptin show that it may be up to a third less effective than has been claimed.

The doctors, from the New Zealand Government's Pharmaceutical Management Agency (Pharmac), said in the journal that they may have identified a new case of publication bias – in which drug companies publish only trial results that are favourable, the Guardian newspaper reported.

The missing data is important and related to a trial involving nearly 1000 women, wrote Dr Scott Metcalfe and his colleagues at Pharmac.

In the trial, the North Central Cancer Treatment Group (NCCTG), one group of women with early breast cancer were given Herceptin at the same time as chemotherapy drugs called taxanes. Another group were given Herceptin after they had finished chemotherapy.

The results from those given Herceptin and taxanes concurrently were good – they cut the number of breast cancers that recurred by a third – and have been published, said the researchers.

But results from the women who were given taxanes followed by Herceptin – the method used in the UK – have not been published in a peer-reviewed journal.

Experts were aware of both results, as they featured in an oral presentation at a cancer meeting in 2005 and on a slide presentation on a website.

What they showed, said the Pharmac doctors, was that only a comparatively small number of cancers were prevented from coming back and, statistically, there was a reasonable chance that Herceptin did not protect the women at all.

"The selective release of data from the NCCTG study has far-reaching implications for women with 'Herceptin-susceptible' early breast cancer," the doctors said.

"Without these data. . . (Herceptin) seems more effective than it probably is," wrote Dr Metcalfe. With the missing data the trial "shows a treatment effect one-third less than initially estimated".

Another big Herceptin trial, called Hera, looked at the use of the drug following chemotherapy instead of at the same time and had very positive results.

Roche, the maker of Herceptin, said the NCCTG trial was sponsored by the National Cancer Institute in the US. There was a pre-agreed trial protocol and an independent monitoring committee oversaw the results.

It was up to the investigators to publish the data, said Roche, adding: "Four large trials involving more than 13,000 patients have consistently shown that Herceptin extends survival when administered either sequentially or concurrently with adjuvant chemotherapy."