It has been demonstrated that, in early breast cancer, there is no survival benefit to additional treatment once a patient has achieved a pathologic complete response (pCR). Together with the well-established prognostic association between pCR and survival, this presents a strong rationale for escalation/deescalation of neoadjuvant treatment based upon response.
See related article by Spring et al., p. 2838
In this issue of Clinical Cancer Research, Spring and colleagues, in what is the largest individual patient-level meta-analysis to date, examined nearly 28,000 cases across 52 neoadjuvant breast cancer trials. (1) As in multiple other studies, they show pathologic complete response (pCR) to be reliably associated with improved overall survival. The HR of 0.22 (which held true when only randomized clinical trials were included, HR 0.31) is consistent with previously reported work. For triple-negative and HER2+ disease, the probability intervals are very tight, but for hormone-positive disease, the probability intervals were wide. This is likely because hormone-positive disease is heterogeneous, even for larger tumors. In the I-SPY2 trial, a multigene test was used to exclude molecularly low risk disease, where risk of recurrence is often later (after 5 years), and where chemotherapy adds little, if any, benefit (2). In I-SPY2, achieving pCR, regardless of subtype, or type of therapy, including 10 novel targeted agents, was associated with an improved event-free and distant metastasis–free survival with a HR of 0.2 (3), demonstrating the importance of patient selection and biomarkers.
What is most impactful about this new meta-analysis is the comparison of 1,601 patients assigned to additional chemotherapy after achieving pCR with 18,462 who achieved pCR but received no subsequent adjuvant therapy after surgery. In terms of mortality reduction, the authors found no further value of additional therapy in patients who had already achieved pCR. The HR for event-free survival among pCR versus non-pCR patients was 0.36 for both of these groups.
In oncology, we have been wedded to the evidence generated by myriad adjuvant trials. These data have made clinicians reluctant to use anything less than the “standard therapy.” However, the adjuvant approach has limitations. It only allows the study of populations of patients and provides no short-term indicators of response. The neoadjuvant approach provides direct feedback on response, allowing as Spring and colleagues have done, to study women who received the first chemotherapy regimen prior to surgery, and the second regimen after. That further adjuvant therapy after achieving pCR carries no benefit runs counter to the long-held dictum that the full regimen must be delivered. In this case, more is not better, it is simply more toxic.
There has been a fair amount of controversy about whether early endpoints such as complete response should be used to determine the effectiveness of new agents and combinations and whether we can indeed tailor therapy based on response. The debate has even attracted mainstream attention.
In January, an editorial in the New York Times raised concern about the FDA approving new medicines/devices on the basis of surrogate or early clinical endpoints (4). The implication was that surrogate endpoints are potentially hazardous shortcuts.
The purpose of surrogate or early endpoints is to accelerate the pace of learning, or said differently, to make “knowledge turns” shorter. If you are suffering from a life-threatening disease where the treatments are toxic, you hope that your care team and the scientists studying your disease will have a sense of urgency, because your life is on the line. One would hope that there are efforts to move beyond standard ways of testing that require 10–15 years for an effective therapeutic to get to market, to speed development, and get more effective treatments to patients more quickly and efficiently.
In the 1980s, the sense of urgency regarding the AIDS epidemic led to a very successful strategy to speed development, one that was predicated on an early endpoint. T-cell counts became the early surrogate endpoint, rather than death from AIDS. This simple change dramatically accelerated the ability to tell whether a drug was working, and fueled the paradigm shift where AIDS became a treatable chronic disease rather than a death sentence. Today there are more than 200 retroviral drugs approved. Surrogates are still being used to rapidly test promising new therapeutic advances in cardiology to avoid death from fatal heart attack (5). In fact, early endpoints generated from integrity-based trials benefit patients and science.
In breast cancer, the implications of the Spring and colleagues' meta-analysis with the I-SPY2 findings are enormous. The neoadjuvant path is extremely valuable for two major reasons. First, we have proven and continue to demonstrate that response (in clinically and molecularly high-risk disease) is the primary predictor of the patient's long-term outcome. The I-SPY consortium and others have spent 20 years striving to bring effective drug treatment to patients earlier in the course of disease, where excellent response translates into a cure, not just additional months of survival. Complete pathologic response is a reliable early endpoint providing critical information that allows us to learn, early in the course of treatment, whether a drug is working. We are continuing to work to refine and improve the early endpoints using the more granular residual cancer burden, refining and integrating imaging endpoints of response, and emerging biomarkers such as circulating tumor DNA (6–8). Response to treatment is now dictating adjuvant treatments and trials.
Second, we can rapidly evaluate new and promising therapies, and escalate if treatment is suboptimal, avoiding additional toxic therapy if responses are excellent. This is about getting the right drug to the right patient at the right time. If we remove the tumor first, we cannot optimize treatment, and often make surgical therapy unnecessarily aggressive.
Indeed, this can be a watershed moment to pivot and design trials with the goal of optimizing individual outcomes by establishing a pathway to deescalate and escalate therapy in the neoadjuvant setting.
This is an experiment that needs to be run, and the I-SPY team is planning to do just that (Fig. 1). In the near future, we will introduce I-SPY2.2, which is designed to achieve the best outcomes with the least toxicity, and maximize the potential of the targeted therapies in development. Such a strategy allows treatment to stop at the end of the regimen when pCR is predicted and to advance to increasingly targeted therapies when complete response is not achieved.
It is essential that there be a regulatory path forward to make sure that we can get effective and affordable agents to the people most likely to benefit as quickly as possible, and minimize less effective or more toxic treatments. The ability to adapt treatment to response allows us to make clinical trials more patient-centered. There are hundreds of potential new therapies in development. What we need is an efficient system to prioritize the best treatments and eliminate suboptimal options. Fortunately, the FDA has exhibited strong leadership in advancing our regulatory system to meet modern demands.
It is critical that early endpoints be carefully developed, but it is equally important that our scientific advances include the ability to more rapidly measure whether drugs are working, so we increase the chance of success, with less toxicity. The scientific, regulatory, and clinical enterprise, and all of us who work in it, owe this to our patients.
Disclosure of Potential Conflicts of Interest
L.J. Esserman is an unpaid board member of the Quantum Leap Healthcare Collaborative that is the sponsor of the I-SPY 2 TRIAL and reports receiving other remuneration from the Medical Advisory Panel for Blue Cross/Blue Shield. No other potential conflicts of interest were disclosed.
This article references the collaborative work of the entire I-SPY2 leadership team and the entire network of investigators. The design improvements to I-SPY2 were supported by a P-01 CA 210961 grant from the Clinical Trials Branch/Cancer Imaging Program of the NCI: “I-SPY2+: Evolving the I-SPY 2 TRIAL to include MRI directed, adaptive sequential treatment to optimize breast cancer outcomes.”