In this edition of “How I Will Treat My Next Patient,” I highlight two presentations from the recent San Antonio Breast Cancer Symposium (SABCS) that will likely change practice for some breast cancer patients – even before the ball drops in Times Square on New Year’s Eve.
Residual cancer burden
Dr. Alan P. Lyss
Researchers reported a multi-institutional analysis of individual patient-level data on 5,160 patients who had received neoadjuvant chemotherapy (NAC) for localized breast cancer at 11 different centers. They found that residual cancer burden (RCB) was significantly associated with event-free (EFS) and distant recurrence-free survival. The value of calculating RCB was seen across all breast cancer tumor phenotypes (SABCS 2019, Abstract GS5-01).
RCB is calculated by analyzing the residual disease after NAC for the primary tumor bed, the number of positive axillary nodes, and the size of largest node metastasis. It is graded from RCB-0 (pCR) to RCB-III (extensive residual disease).
Both EFS and distant recurrence-free survival were strongly associated with RCB for the overall population and for each breast cancer subtype. For hormone receptor–positive/HER2-negative disease there was a slight hiccup in that RCB-0 was associated with a 10-year EFS of 81%, but EFS was 86% for RCB-I. Fortunately, the prognostic reliability of RCB was clear for RCB-II (69%) and RCB-III (52%). The presenter, W. Fraser Symmans, MD, commented that RCB is most prognostic when higher levels of residual disease are present. RCB remained prognostic in multivariate models adjusting for age, grade, and clinical T and N stage at diagnosis.
Residual cancer burden linked to long-term survival
How these results influence practice
After neoadjuvant chemotherapy in patients with localized breast cancer, we struggle when patients ask: “So, doctor, how am I likely to do?” We piece together a complicated – and inconsistent – answer, based on breast cancer subtype, original stage of disease, whether pCR was attained, and other factors.
For patients with triple-negative breast cancer, we have the option of adding capecitabine and/or participation in ongoing clinical trials, for patients with residual disease after NAC. Among the HER2-positive patients, we have data from the KATHERINE, ExtaNET, and APHINITY trials that provide options for additional treatment in those patients, as well. For patients with potentially hormonally responsive, HER2-negative disease, we can emphasize the importance of postoperative adjuvant endocrine therapy, the mandate for continued adherence to oral therapy, and the lower likelihood of (and prognostic value of) pCR in that breast cancer subtype.
Where we previously had a complicated, nuanced discussion, we now have data from a multi-institutional, meticulous analysis to guide further treatment, candidacy for clinical trials, and our expectations of what would be meaningful results from additional therapy. This meets my definition of “practice-changing” research.
APHINITY follow-up
APHINITY was a randomized, multicenter, double-blind, placebo-controlled trial that previously demonstrated that pertuzumab added to standard chemotherapy plus 1 year of trastuzumab in operable HER2-positive breast cancer was associated with modest, but statistically significant, improvement in invasive disease–free survival (IDFS), compared with placebo and chemotherapy plus trastuzumab (hazard ratio, 0.81; P = .04). When the initial results – with a median follow-up of 45.4 months – were published, the authors promised an update at 6 years. Martine Piccart, MD, PhD, provided that update at the 2019 SABCS (Abstract GS1-04).
In the updated analysis, overall survival was 94.8% among patients on the pertuzumab arm and 93.9% among patients taking placebo (HR, 0.85). IDFS rates were 90.6% versus 87.8% in the intent-to-treat population. The investigator commented that this difference was caused mainly by a reduction in distant and loco-regional recurrences.
Central nervous system metastases, contralateral invasive breast cancers, and death without a prior event were no different between the two treatment groups.
Improvement in IDFS (the primary endpoint) from pertuzumab was most impressive in the node-positive cohort, 87.9% versus 83.4% for placebo (HR, 0.72). There was no benefit in the node-negative population (95.0% vs. 94.9%; HR, 1.02).
In contrast to the 3-year analysis, the benefits in IDFS were seen regardless of hormone receptor status. Additionally, no new safety concerns emerged. The rate of severe cardiac events was below 1% in both groups.
APHINITY 6-year data: Benefit ongoing in HER2+ early BC, no significant OS benefit
How these results influence practice
“Patience is a virtue” appeared for the first time in the English language around 1360, in William Langland’s poem “Piers Plowman.” They are true words, indeed.
When the initial results of APHINITY were published in 2017, they led to the approval of pertuzumab as an addition to chemotherapy plus trastuzumab for high-risk, early, HER2-positive breast cancer patients. Still, the difference in IDFS curves was visually unimpressive (absolute difference 1.7% in the intent-to-treat and 3.2% in the node-positive patients) and pertuzumab was associated with more grade 3 toxicities (primarily diarrhea) and treatment discontinuations.
An optimist would have observed that the IDFS curves in 2017 did not start to diverge until 24 months and would have noted that the divergence increased with time. That virtuously patient person would have expected that the second interim analysis would show larger absolute benefits, and that the hormone receptor–positive patients (64% of the total) would not yet have relapsed by the first interim analysis and that pertuzumab’s benefit in that group would emerge late.
That appears to be what is happening. It provides hope that an overall survival benefit will become more evident with time. If the target P value for an overall survival difference (.0012) is met by the time of the third interim analysis, our patience (and the FDA’s decision to grant approval for pertuzumab for this indication) will have been amply rewarded. For selected HER2-posiitve patients with high RCB, especially those who tolerated neoadjuvant trastuzumab plus pertuzumab regimens, postoperative adjuvant pertuzumab may be an appealing option.
Dr. Lyss has been a community-based medical oncologist and clinical researcher for more than 35 years, practicing in St. Louis. His clinical and research interests are in the prevention, diagnosis, and treatment of breast and lung cancers and in expanding access to clinical trials to medically underserved populations.