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Community Clinical Cases: Immunotherapy in Triple Negative Metastatic Breast Cancer

A Case Presentation by Dr Gregory Vidal, West Cancer Center

Immunotherapy is a type of cancer treatment that stimulates the body’s immune system to recognize, attack, and kill cancer cells. Recently, immunotherapy has emerged as a new treatment option for breast cancer patients lacking expression of estrogen and progesterone hormone receptors as well as human epidermal growth factor receptor 2 (HER2). These patients are typically referred to as having ‘triple negative’ breast cancer, and in the past, chemotherapy was generally the only treatment option in this setting. At the Total Health 2023 Community Cases Memphis Conference, Dr Gregory Vidal from West Cancer Center presented a case discussion on the use of immunotherapy in a patient with triple negative breast cancer (TNBC).

Case Overview

Dr Vidal described the case of a 50-year-old, otherwise healthy woman, who presents with a breast lesion that was discovered on a routine mammography screening. A biopsy of the lesion showed a grade 2, 5.1 cm invasive ductal carcinoma. Additional testing showed it to be estrogen and progesterone receptor negative (ER/PR <1%) and it was deemed HER2 negative by immunohistochemistry (IHC=0); testing for an immunotherapy biomarker termed programmed death ligand 1 (PD-L1) was also negative (CPS 0). The patient was negative for distant metastasis and lymph node involvement on imaging. On genetic testing, she was also negative for germline BRCA1/2 mutation. Her performance status was good (ECOG PS 0), and her final diagnosis was stage 2 TNBC (T3 N0 M0). The treatment team decided that systemic therapy was appropriate for this patient before surgery (termed “neoadjuvant therapy”). Dr Vidal noted that the most appropriate neoadjuvant treatment for this patient is with the immunotherapy agent pembrolizumab, in combination with chemotherapy (paclitaxel + carboplatin) followed by pembrolizumab in combination with anthracycline + cyclophosphamide, based upon findings from the KEYNOTE 522 trial.

The KEYNOTE 522 Study

Dr Vidal detailed the design of the KEYNOTE 522 study, a phase III trial that enrolled adult patients with TNBC that was stage T1c with lymph node involvement, or stage T2 – T4 without nodal involvement, and who had been assessed for their PD-L1 status. The patients were randomized to treatment with pembrolizumab or placebo before and after surgery, in addition to standard of care treatment (carboplatin/paclitaxel à anthracycline/cyclophosphamide, as above). The primary endpoint of the study was the percentage of patients achieving a pathologic complete response (pCR). Achieving a pCR is a key outcome in TNBC, as patients with pCR have better overall and recurrence-free survival outcomes (i.e., a “favorable prognostic factor”).

Dr Vidal reviewed the results of the trial, which showed a significant improvement in the percentage of patients achieving a pCR on pembrolizumab versus those on placebo (64.8% vs. 51.2%; p=0.00055). Event-free survival (EFS) at a median 39.1 month follow up was also significantly better with pembrolizumab (84.5% vs. 76.8%). Notably, in subgroup analysis, there was a similar benefit in EFS over placebo for patients with or without lymph node involvement, and regardless of their PD-L1 expression. There was also a benefit of pembrolizumab in overall survival observed (89.7% vs. 86.9%) at the most recent analysis. Another important finding from a pre-specified, exploratory analysis which Dr Vidal noted was that outcomes were similar between the treatment groups for patients who achieved a pCR (EFS, 94.4% vs. 92.5%) and, as expected, were worse for patients who did not achieve pCR (67.4% vs. 56.8%), although EFS with pembrolizumab was still better than that observed for placebo.

Dr Vidal also reviewed the safety results from the trial, which are important to consider as patients continue to receive pembrolizumab over an extended period as adjuvant therapy. When considering the combined treatment phases (neoadjuvant and adjuvant together) there was a similar incidence of adverse events (AEs) and grade 3 to 5 AEs in the pembrolizumab and placebo arms. When considering the adjuvant treatment phase only, the percentage of patients with any event (53.7% vs. 48.6%), or a grade 3 to 5 AEs (6.3% vs. 2.7%) was higher with pembrolizumab versus placebo. Immune-related AEs (IRAEs) and infusion reactions in the combined treatment phases, as expected, were higher with pembrolizumab versus placebo (overall, 43.6% vs. 21.9%; grade 3-5, 14.9% vs. 2.1%). Dr Vidal noted that some of these IRAEs include hypothyroidism and adrenal insufficiency, which can require lifelong treatment.

Case Continued

The patient in the case received neoadjuvant therapy with the KEYNOTE 522 regimen (paclitaxel/carboplatin + pembrolizumab) followed by doxorubicin/cyclophosphamide + pembrolizumab) and she achieved a pCR at definitive surgery. As in the 522 study, she was then initiated on adjuvant therapy with pembrolizumab at 3 weekly intervals (Q3W). The patient remains on therapy with pembrolizumab at last follow up.

Unanswered Questions

Despite the positive findings of KEYNOTE 522, and the favorable results in this TNBC patient having achieved a pCR, Dr Vidal noted that there remain many unanswered questions in this setting. For example, it remains unclear how long patients should be continued on adjuvant pembrolizumab (i.e., after surgery), as immunotherapy does entail significant risk, including IRAEs that may require lifelong treatment. Because the outcomes are very good for both placebo and pembrolizumab treated patients who achieve a pCR, it can be debated whether continued adjuvant pembrolizumab offers any substantive benefit in this scenario if patients achieve a pCR. Dr Vidal noted that he would, at present, be inclined to continue the immunotherapy in patients achieving a pCR, if the patient is tolerating the treatment.

Another consideration is that the optimal treatment approach may differ if, unlike the case example, the patient had a BRCA1/2 mutation; such patients may benefit from a PARP-inhibitor therapy such as Olaparib. Indeed, one year of adjuvant Olaparib has been shown to improve both progression-free and overall survival in patients with BRCA1/2 mutation. Dr Vidal noted that based on the available data he would be inclined to even combine adjuvant Olaparib with immunotherapy, particularly for higher-risk patients that did not achieve a pCR.

Dr Vidal also emphasized that the optimal therapy has not been established for those patients without a BRCA1/2 mutation who do not achieve pCR after neoadjuvant treatment. He noted that these patients are at higher risk for recurrence and overall poorer outcomes based on their residual cancer burden (RCB). For example, for those with an RCB of 3 (meaning the highest level of residual disease) the chance for a TNBC patient to be disease-free at 5 years is only 30%. For these patients, Dr Vidal noted that other therapies, such as adjuvant capecitabine, may be an option, and if it is possible to combine with immunotherapy, he would also combine therapies, as these patients clearly require additional treatment to prevent recurrence.


Quick Summary

  • For patients with TNBC, the addition of immunotherapy to standard of care neoadjuvant chemotherapy improves the percentage of patients achieving a pathological complete response (pCR).

  • Patients who achieve a pCR have significantly better outcomes versus those who do not.

  • Findings of the KEYNOTE 522 trial show a benefit of adding the immunotherapy pembrolizumab in both node negative and node positive patients, and regardless of their PD-L1 status.

  • For patients achieving a pCR in KEYNOTE 522, event-free survival (EFS) was largely similar with or without the addition of pembrolizumab.

  • For patients not achieving a pCR in KEYNOTE 522, EFS was significantly worse overall, but was still improved over chemotherapy alone with addition of pembrolizumab.

  • Patients who do not achieve a pCR after neoadjuvant therapy are at a higher risk for recurrence and poor outcomes, based on their level of residual cancer burden (RCB status).

  • The optimal management of TNBC patients with a BRCA1/2 mutation, and for those not achieving a pCR is not established.

  • PARP inhibitor therapy (for those with a BRCA1/2 mutation) and adjuvant capecitabine (for those not achieving a pCR), possibly in combination with immunotherapy, may be options for these patients.


See more from the 2023 Community Cases Memphis Conference here.

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