Myelopreservation Possible With CDK4/6 Inhibitor Trilaciclib in TNBC

Wayne Kuznar
Published: Thursday, Dec 06, 2018

Joyce A. O’Shaughnessy, MD
Joyce A. O’Shaughnessy, MD
A longer duration of chemotherapy exposure was possible in patients with metastatic triple-negative breast cancer (mTNBC) who received trilaciclib, an investigational CDK4/6 inhibitor, in addition to gemcitabine and carboplatin (GC) compared with GC alone. Despite the longer duration of GC, the incidence of major adverse hematologic events (MAHE) was significantly lower in trilaciclib recipients compared with those who received chemotherapy without trilaciclib, according to results of a randomized phase II study.

In addition, tumor response rates were higher and there was a trend toward longer progression-free survival (PFS) in patients receiving 1 or 2 doses of trilaciclib per cycle in addition to GC compared with chemotherapy alone.

Preliminary data from the phase II trial showed that a median of 20.0 weeks of GC could be given when trilaciclib was dosed once per cycle and a median of 19.0 weeks of GC was possible when dosed twice per cycle, compared with a median of 14.4 weeks with chemotherapy alone,1 reported Joyce O’Shaughnessy, MD, and colleagues at the 2018 San Antonio Breast Cancer Symposium.

“Adjusting for the duration of chemotherapy, trilaciclib demonstrated multi-lineage myelopreservation benefits,” the study authors stated in their poster presentation.

“Trilaciclib prevented or delayed clinically significant MAHE,” said O’Shaughnessy, chair of Breast Cancer Research, Baylor-Sammons Cancer Center, Dallas. “It was these MAHE, prolonged neutropenia, dose reductions, platelet transfusions, red blood cell (RBC) transfusions, that seem to be impacted.”

The incidence of MAHE was a prespecified exploratory composite measure of the effect of trilaciclib, and included all-cause hospitalizations, dose reductions, febrile neutropenia, prolonged severe neutropenia, and red blood cell and platelet transfusion. Patients who received chemotherapy alone had a higher rate of MAHE (19%) relative to patients who received trilaciclib (13% with 1 dose per cycle and 9% with 2 doses per cycle), with the difference between the trliaciclib groups and the GC group significant (P = .0181). There were significant decreases in all-cause hospitalizations (P = .0099), prolonged severe neutropenia (P =.0406), and RBC transfusions on/after 5 weeks (P = .0197) in the trilaciclib groups versus GC alone.

The median cumulative dose of gemcitabine increased from 7,306.2 mg/m2 in the chemotherapy alone to 9,643.7 mg/m2 and 10,959.6 mg/m2 in the groups receiving 1 and 2 doses of trilaciclib per cycle, respectively. A similar increase in the median total carboplatin dose was observed—15 AUC with chemotherapy alone versus 20 AUC in both trilaciclib groups.

Among response evaluable patients, those randomized to the triplet had an objective response rate (ORR) of 36.7% to 43.3%, depending on the trilaciclib dosing schedule, compared with 29.2% with GC alone. All responses in all groups were partial responses. Median PFS among the intent-to-treat (ITT) population was 7.9 months in the 2 trilaciclib arms combined compared with 5.4 months in the patients randomized to GC alone (P = .0189). The probability of remaining progression-free at 6 months was higher for patients receiving trilaciclib versus GC alone (69% vs. 43%; P = .0169).

Trilaciclib is being developed to reduce the myelosuppressive effects of chemotherapy and preserve immune system function rather than directly target tumor proliferation,” the investigators said. Patents with mTNBC were chosen for the study because it is predominantly a functionally CDK4/6-independent disease and because cytotoxic chemotherapy is the backbone of treatment for mTNBC and is often limited by myelotoxicities.

The trial included a total of 98 patients with mTNBC in the US and European Union who had received 0 to 2 prior systemic cytotoxic therapies in the locally recurrent or metastatic setting and who had no symptomatic brain metastases.

Patients were randomized 1:1:1 to: GC alone (G: 1000 mg/m2; C: AUC 2) using a standard schedule (days 1 and 8 every 21 days), trilaciclib (240 mg/m2) administered on the same days as standard GC above, an alternate schedule that dosed trilaciclib on days 1, 2, 8, and 9 and GC on days 2 and 9 every 21 days.

On the days when both tilaciclib and GC were scheduled, tilaciclib was administered intravenously prior to GC infusion. Prophylactic growth factors were not allowed in cycle 1; otherwise supportive care was allowed as needed.

The median age of the 102 patients enrolled (4 withdrew consent and were not treated) was 57 years, all had an ECOG performance status of 0 (53%) or 1 (47%), 62.7% had received no systemic therapy in the recurrent/metastatic setting and 37.3% received 1 or 2 prior lines. Six (5.9%) had brain metastases and 25.5% had liver metastases at baseline. Tumor subtyping showed basal-like in 52.2%.

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