NEW YORK (Reuters Health) – For women with HER2-positive breast cancer, trastuzumab is as beneficial in those with invasive lobular disease as those with invasive ductal carcinoma, according to a multinational study.
“The present analysis shows no evidence of a difference in pattern of disease relapse or in the magnitude of trastuzumab benefit for the two groups of patients,” the researchers conclude in their report in the Journal of Clinical Oncology online April 15.
Dr. Martine Piccart-Gebhart, at the Institut Jules Bordet in Brussels, Belgium, and colleagues explain that up to 15% of breast cancer cases are invasive lobular carcinoma (ILC), which differs from invasive ductal carcinoma (IDC) in natural history and clinicopathologic features. In particular, classic cases of ILC are believed to be HER2-negative, but it is now recognized that about 5% are positive.
However, there is little information about the magnitude of benefit of anti-HER2 therapies in HER2-positive ILC. The team therefore compared outcomes among breast cancer patients in the Herceptin Adjuvant (HERA) trial who were assigned to 1 year of trastuzumab treatment or observation only after chemotherapy. While 3213 patients had IDC, 187 had ILC.
After a median follow up of 4 years, disease-free survival favored trastuzumab over observation, with hazard ratios of 0.63 in the ILC group and 0.77 in the IDC group, the investigators found. The HRs were not significantly different with a p value for interaction of 0.49.
Similarly, the corresponding hazard ratios for overall survival in the two arms were 0.60 and 0.86 (p for interaction = 0.29).
The authors also found that the site-specific pattern of relapse was similar in the two histologic subtypes.
Summing up, Dr. Piccart and colleagues draw three “important” conclusions from their findings: “First, a diagnosis of lobular histologic subtype does not equal HER2 negativity and HER2 testing should be carried out in these cases.”
“Second,” they continue, “patients diagnosed with early-stage, HER2-positive ILC should be offered 1 year of adjuvant trastuzumab. And finally, HER2-positive ILC treated with trastuzumab will derive a benefit of a magnitude similar to patients with the IDC histologic subtype.”
Dr. Piccart was unavailable to comment on the findings, her office told Reuters Health, because she was traveling.
SOURCE: Magnitude of Trastuzumab Benefit in Patients With HER2-Positive, Invasive Lobular Breast Carcinoma: Results From the HERA Trial
J Clin Oncol 2013;31.
