Standard chemotherapy shows no benefit for certain types of colon cancer

Patients with certain types of colon cancer do not benefit from standard chemotherapy, new research shows, and the treatment may even cut their survival time. The findings back up the findings of a 2003 study.

The researchers looked at the response to chemotherapy of more than 1000 patients with colon cancer, 15% of whom had the usually less aggressive dMMR type of tumour. These tumours occur later in life than other colon tumours and are associated with a better overall prognosis, but they lack the ability to repair DNA damage caused by chemotherapy. The rest of the patients had tumours with other genetic variations and chromosomal instability.

In 2003 research in the New England Journal of Medicine ((New England Journal of Medicine 2003;349:247-257) reported that patients with dMMR tumours did not benefit from chemotherapy. The new study, which will be presented at the 44th annual meeting of the American Society in Clinical Oncology being held from 30 May to 3 June 2008, in Chicago, Illinois, included 1027 patients who were randomly assigned to receive fluorouracil chemotherapy or no chemotherapy.

Among patients with chromosomally unstable tumours (84% of the patients), 75% of patients who underwent chemotherapy survived five years, whereas the five year survival rate was 66% in those who were given no chemotherapy. Among patients with dMMR tumours (16% of all patients), the five year survival rate was 75% in those who underwent chemotherapy and 93% in those who had no chemotherapy.

The findings are particularly relevant for patients with stage II disease, who would normally be treated with single agent fluorouracil.

“[This information] could save patients the toxicity, inconvenience, and expense of treatment from which they will receive no benefit,” said Daniel Sargent, of the Mayo Clinic and lead author of the new study.

The reasons for the poorer outcome among patients with dMMR tumours who undergo chemotherapy are not yet clear. Because these cancer cells cannot repair DNA damage, mutations induced by chemotherapy may lead to a more aggressive cancer, the authors say. Alternatively, chemotherapy may curb the immune response, which would normally hinder cancer growth, they say.