In this JCO Precision Oncology Article Insights episode, Mitchell Elliot provides a summary on "Prediction of Benefit From Adjuvant Pertuzumab by 80-Gene Signature in the APHINITY (BIG 4-11) Trial," by Krop, et al published on January 18th, 2024.

TRANSCRIPT

Mitchell Elliott: Hello and welcome to JCO Precision Oncology Article Insights. I'm your host, Mitchell Elliott, an ASCO Journal Editorial Fellow. Today, I will be providing a summary of the article titled "Prediction of Benefit from Adjuvant Pertuzumab by 80-Gene Signature in the APHINITY (BIG 4-11) Trial" by Dr. Ian Krop on behalf of the APHINITY Steering Committee and Investigators.

HER2 epidermal growth factor receptor 2 positive, or HER2 positive breast cancer is characterized by overexpression of the HER2 protein. HER2 is an extracellular receptor that binds with itself and other proteins on the cell surface to facilitate rapid growth and division of cancer cells. Historically, HER2 positive breast cancer carried a worse prognosis than other subtypes. Anti-HER2 therapy with the monoclonal antibody trastuzumab in combination with chemotherapy has been shown to significantly improve clinical outcomes. Pertuzumab, another anti-HER2 monoclonal antibody, binds to a different site on the HER2 protein and has been shown to further disrupt HER2 signaling and improve clinical outcomes.

Primary results from the APHINITY trial, this trial, served as the basis for dual HER2 blockade, combining trastuzumab and pertuzumab with chemotherapy in the adjuvant setting. This data helped establish dual HER2 blockade as the standard of care in many jurisdictions around the world. Understanding patients who do not derive benefit from the additional anti-HER2 therapy is paramount for delivering personalized and effective care while minimizing treatment-related side effects. Understanding the underlying biology of patients who do not drive a response may provide insight into areas of future drug development and integration of novel therapies into future clinical trials.

The clinical definition of HER2 positivity encompasses those that are most likely to have HER2-driven tumors, but previous work has demonstrated that this clinical-pathologic definition does not accurately reflect the molecular heterogeneity of this subtype. These authors completed a translational secondary analysis of the phase III APHINITY trial using nested case-control methods with RNA-seq data derived from primary tumors of patients enrolled in this trial. Both the MammaPrint and Blueprint classifiers are commercially available assays run on microarray data using previously published and validated gene sets. MammaPrint classifies tumors as high or low risk, while Blueprint classifies tumors into luminal, basal-like, or HER2 subtypes. Luminal A tumors are MammaPrint low risk luminal classification, while luminal B tumors are classified as MammaPrint high risk with conventional luminal classification.

In order to facilitate these analyses, RNA-seq data was converted into pseudo microarray-based sequencing using a bridge study from an independent cohort of 75 patients. Conventional Blueprint scores for luminal type, HER2 type, or basal type were calculated for each sample. The subtype with the highest score of the three was the conventional subtype reported for the tumor. The Blueprint subtype was further sub-stratified as a single-activated or dual-activated subtype. Single-activated samples represented the dominant enriched pathway in each tumor, while dual-activated subtypes were assigned if there was no statistical difference between the two dominant pathways.

The primary endpoint was invasive disease-free survival, IDFS, and was stratified by genomic subtype and treatment arm. IDFS was defined as the time from treatment random assignment until the date of first recurrence of ipsilateral invasive breast tumor, recurrence of ipsilateral local-regional invasive disease, distant disease recurrence, contralateral invasive breast cancer, or death from any cause. Patients without an event at the last follow-up date were censored. The median follow-up time was 45.4 months. 964 patients were evaluated for MammaPrint and Blueprint subtypes. One patient was excluded as they were low risk by MammaPrint. The final cohort included 963 patients in this nested case-control study with IHC/FISH-defined HER2 positive tumors. Two-thirds of the patients were hormone receptor positive. Most patients were over the age of 35, 83% had lymph node involvement, and 83% of patients received anthracycline-containing chemotherapy.

Blueprint classified 50% of patients as luminal B type, 28% as HER2 positive, and 22% as basal type. Most of the luminal B tumors were single-pathway activated, while only around 50% of HER2 type and basal type tumors had single-activated pathways. Similar clinical and treatment characteristics were observed between the conventional Blueprint subtypes as well as the single and dual-activated subtypes.

Nested case-control inverse probability-weighted corrected multivariate Cox regression analysis revealed no significant difference in IDFS among the different conventional Blueprint subtypes. Conventional Blueprint subtypes were also not prognostic of benefit from the addition of pertuzumab. The authors then investigated whether there was a significant difference in IDFS in patients with only single gene pathway activation. Interestingly, patients classified as Blueprint basal single-activated subtypes were more likely to have an IDFS event, with a hazard ratio of 1.69 and a 95% confidence interval of 1.12 to 2.54. This captures the worst prognosis of molecularly defined basal-like tumors, remembering that all of the patients included in this cohort were, by ASCO-CAP guidelines, HER2 positive. In comparing the benefit from the addition of pertuzumab amongst the patients with single-activated subtype, there was no significant improvement in IDFS events with the addition of pertuzumab. There was a non-significant numerical benefit with the addition of pertuzumab in HER2 single subtype, suggesting that patients with dominant HER2-related signaling may derive more benefit from this combination therapy.

To help account for confounding variables, multivariate analyses were pursued to correct for routine clinical factors such as age, nodal status, hormone receptor status, as well as the use of anthracycline in addition to the conventional and single-activated pathway subtypes. Of all the clinical factors included in these analyses, only nodal status was significantly associated with IDFS in all of the conventional and single-activated subtypes. This reflects the important consideration of both clinical and genomic risk in patient assessment, as both have strong implications on treatment outcomes.

In summary, Blueprint HER2 tumors, which consist of both single and dual pathway-activated tumors, did not clearly distinguish those who derived pertuzumab benefit. There was a further non-significant benefit noted in HER2 single pathway-activated tumors. This suggests that tumors with multiple mitogenic pathways may have an inferior response to HER2 targeted therapy compared to single-activated tumors.

Overall, this article presents further insight into the molecular heterogeneity within the clinical-pathologic defined HER2 positive breast cancer subtype. The use of a commercially available gene signature assay was able to distinguish a subset of patients with a worse overall clinical outcome regardless of treatment received. Further analyses are required to validate and assess the utility in deploying this strategy in the treatment of patients with early HER2 positive breast cancer, but there is a suggestion that the 80-gene signature may refine patient selection, optimize treatment planning, and improve long-term outcomes for this patient population.

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