Women with HER2-positive breast cancer who had high levels of immune cells in their tumours had a decreased risk of cancer recurrence after treatment with chemotherapy alone compared with their counterparts who had low levels of tumour-infiltrating immune cells, according to data presented at the 2014 San Antonio Breast Cancer Symposium.

There was no association between tumour-infiltrating immune cell levels and recurrence-free survival among women who received chemotherapy and the HER2-targeted therapy trastuzumab.

“There are two main findings from our study,” said Edith A. Perez, MD, deputy director at large for the Mayo Clinic Cancer Centre and the Serene M. and Frances C. Durling professor at Mayo Clinic College of Medicine, based in Jacksonville, Florida.

“First, patients with high levels of tumour-infiltrating immune cells did well with chemotherapy alone. Second, the level of tumour- infiltrating immune cells had no impact on the benefit of adding trastuzumab to chemotherapy.”

Among 489 women with early-stage, HER2-positive breast cancer who were randomised in the phase III clinical trial N9831 to chemotherapy alone, those with high levels of tumour-infiltrating immune cells had an 80 percent decreased chance of disease recurrence after a median follow-up of 4.4 years.

Among the 456 patients randomised to chemotherapy and trastuzumab, the chance of disease recurrence was the same irrespective of the levels of tumour-infiltrating immune cells.

“We have previously reported that adding trastuzumab to chemotherapy significantly improved recurrence-free and overall survival in N9831,” said Perez. “However, not all patients benefited from addition of trastuzumab, and some did well with chemotherapy alone. These results suggest that levels of tumour-infiltrating immune cells may provide a biomarker to identify patients who might do well without trastuzumab, but we must conduct additional large clinical trials before we can consider changing clinical practice and omitting HER2-targeted therapy from the treatment regimens for patients who have high levels of tumor-infiltrating immune cells.

“We were somewhat surprised by our finding that high levels of tumour-infiltrating immune cells were not associated with increased benefit among women receiving trastuzumab because a previous study had shown that this was the case,” continued Perez. “However, the previous study had many fewer cases and lower statistical power.”

Perez and colleagues analysed primary tumour samples obtained prior to patients initiating chemotherapy or chemotherapy and trastuzumab treatment. Samples were considered to have high levels of tumour-infiltrating immune cells if 60 percent or more of cells in the sample section being analysed were immune cells.

In future analysis, Perez says that she and her colleagues will look at the different subtypes of immune cells, and determine if any subtype in particular is associated with improved patient outcomes.

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Source: SABCS