SAN ANTONIO (FRONTLINE MEDICAL NEWS) – Among patients receiving trastuzumab plus lapatinib neoadjuvant therapy for HER2-positive early breast cancer, amplification of ERBB2 was predictive of a pathologic complete response (pCR), according to findings presented at the San Antonio Breast Cancer Symposium.

However, ERBB2 mRNA expression and PAM50-enriched HER2 better predicted pCR, said lead study author Cristos Sotiriou, MD, of the Breast Cancer Translational Research Laboratory at the Institut Jules Bordet in Belgium

High genomic instability was associated with a higher pCR rate in patients with estrogen receptor–positive tumors, but copy number alterations (CNAs) were not associated with event-free survival (EFS).

In the large phase 3 NeoALTTO trial, lapatinib combined with trastuzumab in the neoadjuvant setting nearly doubled the pCR rate as compared with either agent used alone. The 3-year EFS was also improved with dual HER2 blockage versus single HER2 therapy (84% for the combination, hazard ratio, 0.78; P = .33 vs. 78% for lapatinib alone and 76% for trastuzumab alone, HR, 1.06; P = .81 for both).

The researchers of this trial also found that pCR was a surrogate for long-term outcome.

“Expression of ERBB2, ESR1, and immune signatures were the main drivers of pCR,” said Dr. Sotiriou.

The main goal of the current study was to investigate the relevance of CNAs for pCR and EFS in this population. A total of 455 patients were enrolled in the NeoALTTO study, and of this cohort, 270 had tumor content that was sufficient to assay for CNAs. Tumor-infiltrating lymphocytes and gene expression were also obtained and the genome instability index was calculated, and 184 samples were included in the final analysis.

Of the cancer genes, only ERBB2 was predictive of pCR.

A total of 159 recurrent CNA regions were identified. ERBB2 amplification was associated with high pCR (P = .0007), but less than ERBB2 expression, and it lost its significance after correcting for ERBB2 expression.

The genome instability index (GII) was defined as the “median absolute deviation of the normalized copy number” and independent of ERBB2 amplification, the pCR rate increased with the GII (P = .03.

Amplification of two regions on 6q23-24 was significantly associated with higher pCR (P = .00005 and P = .00087). One of the segments harbored 39 genes, some with an expression level that was also predictive of pCR. The 6q23-24 segment was associated with pCR in estrogen receptor–positive tumors only (interaction test P = .04).

After multiple testing correction, there were no amplified regions or genes found to be predictive of EFS.

“A novel amplified region on 6q23-24 was shown to be predictive of pCR, in particular for estrogen receptor–positive tumors,” said Dr. Sotiriou. “This may warrant further investigation.”

SOURCE: Sotiriou et al. SABCS Abstract GS1-04