These results suggest tesetaxel plus capecitabine is “a potential new treatment option” for this patient population, said study investigator Joyce O’Shaughnessy, MD, of Baylor University Medical Center and Texas Oncology, both in Dallas.
Dr. Hal Burstein
“This should launch an oral taxane into the clinical space, which will be a nice addition to the toolbox for treating advanced breast cancer, with real upsides for patients,” said Hal Burstein, MD, PhD, of Dana-Farber Cancer Institute and Harvard Medical School, both in Boston, who was not involved in the trial but commented on the results in an interview.
Another commenter was more critical of CONTESSA’s results, which were presented at the 2020 San Antonio Breast Cancer Symposium.
“Three months’ difference in PFS in this setting is meaningless without overall survival [OS] results,” Fatima Cardoso, MD, of Champalimaud Clinical Center in Lisbon, Portugal, said in a question submitted through the virtual meeting’s chat system.
At this point, the OS data are immature, and mature data won’t be available for another couple of years at least, according to the study’s protocol.
Dr. O’Shaughnessy defended the PFS result as being significant, however, saying it was comparable with outcomes seen previously with docetaxel-capecitabine and paclitaxel-gemcitabine combinations.
Other meeting attendees questioned why the waters had been muddied by testing the effects of tesetaxel in combination with capecitabine, albeit at a reduced dose, versus the approved full dose of capecitabine as monotherapy, particularly as a phase 2 trial had shown that tesetaxel demonstrated “significant activity” as monotherapy.
“The reason for the combination versus a monotherapy is because it was designed as a registration trial,” Dr. O’Shaughnessy explained. The trial was designed to be very similar to early taxane studies where docetaxel was assessed with or without capecitabine, or paclitaxel with or without gemcitabine.
“Probably we’re going to be using a doublet for patients who have virulent disease who really need a response,” Dr. O’Shaughnessy explained. She noted that the objective response rate was much higher with the tesetaxel-capecitabine combination than with capecitabine alone, and that result alone is “probably enough that we would utilize a doublet.”
The key thing is that it now gives patients an all-oral option, Dr. O’Shaughnessy said.
“The data are exciting because it would be terrific to have an orally available taxane chemotherapy,” agreed Dr. Burstein. “It is far more convenient for patients and opens access globally in places that do not have adequate resources for administration of IV therapeutics. Also, the data suggest that tesetaxel has a different side effect profile than IV taxane, with less neuropathy and less alopecia.”
Trial design
CONTESSA is an ongoing randomized, controlled trial that started in 2017 and is projected to end in early 2023. It is investigating the use of tesetaxel plus a reduced dose of capecitabine versus the approved dose of capecitabine alone in 685 women with hormone receptor–positive, HER2-negative locally advanced or metastatic breast cancer who had previously been treated with a taxane.
Being intrinsically orally bioavailable and more soluble than the other taxanes means that tesetaxel has a much longer half-life that allows for a “more convenient treatment experience for patients,” Dr. O’Shaughnessy observed.
Indeed, because tesetaxel only needs to be dosed once every 3 weeks, patients in the trial received tesetaxel at 27 mg/m2 only on the first day of a 21-day treatment cycle. This was combined with a reduced, 825-mg/m2 dose of capecitabine, given orally twice-daily on days 2-14 but once daily on the evening of day 1 and on the morning of day 15.
The combination regimen was compared with the recommended full dose of capecitabine alone, 1,250 mg/m2 given orally twice daily on days 2-14 but once daily on the evening of day 1 and on the morning of day 15.
Efficacy and safety
PFS was 9.8 months with tesetaxel plus capecitabine and 6.9 months with capecitabine alone, representing a 2.9-month improvement with the combination (hazard ratio, 0.716; P = .003).
A similar PFS benefit was seen regardless of multiple predefined subgroups, such as age, baseline performance status, duration of disease-free interval before study entry, and the use of CDK4/6 inhibitors.
The objective response rate was 57% with tesetaxel plus capecitabine and 41% with capecitabine alone (P = .0002). The 24-week disease control rate was 67% and 50%, respectively (P < .0001).
The most frequent treatment-emergent adverse event seen with the tesetaxel-capecitabine combination was neutropenia, occurring in 76.9% of patients, compared with 22.6% of patients in the monotherapy arm. Rates of grade 3-4 neutropenia were much higher in the combination arm (32.6% and 38.3%, respectively) than in the monotherapy arm (7.4% and 0.9%, respectively).
The neutropenia seen was “generally manageable,” Dr. O’Shaughnessy said, primarily with dose reductions and granulocyte colony–stimulating factor as needed.
She pointed out that rates of grade 3 or higher neuropathy and grade 2 alopecia were low, a respective 5.9% and 8%, with the combination.
The dose of capecitabine used in the control arm was noted to be higher than that used in usual practice.
“This was because of the global nature of the study and the regulatory requirements globally,” Dr. O’Shaughnessy said.
“The dose-modification scheme was that patients could have a dose reduction at the first sign of grade 2 toxicity,” she added, giving investigators the flexibility to reduce the dose as soon as possible.
This study was sponsored by Odonate Therapeutics. Dr. O’Shaughnessy disclosed consulting fees from AbbVie, Agendia, AstraZeneca, Bristol-Myers Squibb, Celgene, Eisai, Genentech/Roche, Genomic Health, GRAIL, Heron, Immunomedics, Ipsen, Jounce, Lilly, Novartis, Odonate, Pfizer, Puma, and Seagen. Dr. Burstein and Dr. Cardoso had no relevant disclosures.
SOURCE: O’Shaughnessy J et al. SABCS 2020, Abstract GS4-01.