Can new Tukysa data drop unlock its sales potential?

Pfizer has a positive phase 3 trial for its small-molecule HER2 inhibitor Tukysa as first-line maintenance therapy for HER2-positive metastatic breast cancer, raising the prospect of a label extension that could boost take-up of the drug.

The results of the HER2CLIMB-05 show that Tukysa (tucatinib) improved progression-free survival (PFS) compared to placebo when added to the first-line maintenance therapy of choice for HER2-positive breast cancer – trastuzumab and pertuzumab – after induction chemotherapy.

The finding could open up earlier use of Tukysa, which has been approved for a few years as second-line or later therapy for HER2-positive breast cancer that cannot be treated with surgery, as well as for previously-treated HER2-positive metastatic colorectal cancer.

"The positive results from HER2CLIMB-05, combined with Tukysa's known safety profile in later-line settings, underscore its potential to play a meaningful role in front-line maintenance, where it may benefit a broader population of patients with HER2+ disease," commented Pfizer's oncology development head Johanna Bendell.

Pfizer acquired Tukysa as part of its takeover of Seagen for $43 billion in 2023, but sales have been modest, rising just 3% to $234 million in the first half of the year.

That makes it the poor relation to the other main assets in the Seagen takeover – antibody-drug conjugates Padcev (enfortumab vedotin) for bladder cancer and Adcetris (brentuximab vedotin) for blood cancers – which made $967 million and $472 million, respectively, in the same period.

While it's probably fair to say none of the Seagen drugs have performed well enough to justify the price of the acquisition, the new data could transform Tukysa's also-ran status at a time when its growth is being pegged back by steep competition from AstraZeneca and Daiichi Sankyo's HER2-targeting ADC Enhertu (trastuzumab deruxtecan). That product has been expanding its position in HER2-positive breast cancer, as well as other indications, and brought in nearly $2.3 billion in the first half of the year.

Enhertu also now has a chance of moving into the first-line setting, where it is being prepared for filings based on the results of the recently revealed DESTINY-Breast09 study, although that did not include maintenance treatment.

Pfizer, meanwhile, is also looking at moving Tukysa into earlier-stage breast cancer with an adjuvant study in high-risk, HER2-positive breast cancer (CompassHER2 RD), although data from that isn't due until 2028 onwards.