While many doctors consider small tumors less harmful, new data from the international MINDACT breast cancer study suggests otherwise.
In the study, nearly one in four early-stage breast cancer patients with tumors smaller than 1 cm — a little less than half an inch — had aggressive tumors and benefited from chemotherapy after surgery.
Researchers will present the findings at the European Society for Medical Oncology Congress in Madrid, Sept. 8-12.
“Our results challenge the assumption that all small tumors are less serious and do not need adjuvant chemotherapy,” Dr. Konstantinos Tryfonidis, a researcher at the European Organisation for Research and Treatment of Cancer in Brussels, said in a press release. He was the study’s lead author.
MINDACT covered 6,693 women who had early-stage breast cancer between 2007 and 2011. The European Organisation for Research and Treatment of Cancer and Breast International Group conducted the study, which covered nine countries.
A previous analysis showed that 46 percent of the women that Adjvant! Online had deemed at high risk of having their cancer recur were actually at low risk, and did not benefit from chemotherapy. The risk was assessed by the 70-gene signature test MammaPrint.
Researchers decided to analyze the 826 patients in the MINDACT study who had a primary tumor smaller than 1 cm. The team found that 96 patients, or 24 percent, were at low risk of recurrence based on standard tests but at high risk of recurrence based on genetic tests.
Normally, patients who are at low risk of recurrence on standards tests would not be offered chemotherapy, but these patients’ high genomic risk suggested they could benefit from it.
To determine their response to chemotherapy, patients were randomly assigned either to receive or not receive it.
After five years, most patients who had chemotherapy had not experienced a relapse, showing that it had benefited them. Indeed, most were metastasis-free — that is, their cancer hadn’t spread — and disease-free for long periods, and they had high survival rates.
“This study shows that it’s not only tumor size that is important for breast cancer patients, but also tumour biology,” said Dr. Evandro de Azambuja, head of the medical support team at Jules Bordet Institute in Brussels. “All tumors in the study were small – less than 1 cm – and the lymph nodes were free of cancer (node negative), which in principle should be a signal of good prognosis. But nearly one in four patients – those identified as genomic high risk – derived benefit from chemotherapy.”
“We found that nearly one in four patients with small tumors are at risk of distant metastases and do benefit from chemotherapy,” said Dr. Fatima Cardoso, director of the breast unit at the Champalimaud Clinical Center in Lisbon, and the study’s senior author.
“This was striking because based on clinical criteria alone you would say that these tumors are not aggressive and therefore patients do not need chemotherapy,” added Cardoso, who was also the co-principal investigator of the MINDACT study. “But 24 percent of small tumors had an aggressive biology, which shows that not all small tumors are the same.”
“Small node-negative tumors can be very aggressive, even if they are classified as clinical low risk,” Azambuja said. “Tumor biology needs to be taken into account when deciding adjuvant treatments in this patient population. One cannot forget the patient’s age, performance status, comorbidities [other diseases] and preferences during the discussion.”