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Sirtex (ASX:SRX) has announced a post-hoc analysis of data from the 739-patient SIRFLOX and FOXFIRE studies indicates adding Selective Internal Radiation Therapy (SIRT) with liver-directed SIR-Spheres Y-90 resin microspheres to standard first-line mFOLFOX6 chemotherapy for liver-only, or liver-dominant metastatic colorectal cancer (mCRC) in patients with right-sided primary (RSP) tumours, led to a statistically significant and clinically meaningful 4.9 month median overall survival benefit.

This translates into a 36 per cent reduction in the risk of death at any given time, compared to patients who received chemotherapy alone, said the company.

This latest news follows the company announcing a restructure last week, with cost reductions, and confirming its full-year guidance for 2017.

According to Professor Guy van Hazel, study investigator and clinical professor of medicine, University of Western Australia, who presented the new data at the European Society of Medical Oncology’s 19 World Congress on Gastrointestinal Cancer in Barcelona, “This striking and essentially unexpected finding may bring new hope to mCRC patients with liver-only, or liver-dominant tumours that have spread from the right side of the bowel or colon. These cancers are genetically and structurally different from tumours that start on the left side of the colon. Patients with RSP tumours have a worse prognosis for survival and fewer treatment options. They do not respond well to biological therapies such as cetuximab or panitumumab.”

The company said the new data are consistent with a 2016 meta-analysis of 66 studies involving more than 1.4 million CRC patients. It found a significant prognostic impact of primary tumour site on overall survival. Patients with mCRC from a left-sided primary tumour had a 27 per cent reduced risk of death at any given time compared to RSP patients. 

“We had not defined primary tumour ‘sidedness’ as a formal endpoint in the SIRFLOX and FOXFIRE Global studies, which we originally designed in 2005. At that time, scientific understanding of tumour site as a potentially significant variable in the management of CRC was only beginning to emerge. However, we had a strong academic interest in the subject, and were prescient enough to record primary tumour location for every patient we enrolled, and to look at these data as an independent secondary variable in our statistical plan,” said Professor van Hazel.

“We were not alone in our initial conservatism about the effect of tumour site in colorectal cancer. It was only at the 2016 ASCO Annual Meeting, for example, that Prof. Alan Venook of the University of California, San Francisco, stated that, although earlier studies had introduced the idea that tumour location could affect colorectal cancer treatment outcomes, ‘the effect we observed in our retrospective analysis of the Phase III CALGB/SWOG 80405 clinical trial appears to be far greater than we expected,’ and could change the course of disease management.

“Scientific debate must, and will continue on this subject. But if primary tumour sidedness effectively splits colorectal cancer and its metastases into two very different diseases, then treatment paradigms must be carefully reassessed to assure the best possible treatment outcomes for each patient.

“Our findings do require further validation and, subject to this, may support considering earlier use of SIRT for mCRC patients with liver-only,or liver-dominant metastases from right-sided primary tumours.

“It is also important to remember that the data we are reporting now are from first-line studies that combined SIRT with chemotherapy for patients with mCRC, and this does not alter previously established evidence supporting the role of SIRT using SIR-Spheres Y-90 resin microspheres in treating mCRC patients who have failed, or are intolerant to initial chemotherapy that led to the recommendations in the ESMO and NCCN clinical guidelines,” added Professor van Hazel.