Pfizer has stopped a phase 2 study of PF-06835375 in primary immune thrombocytopenia, saying the trial was terminated due to a business decision rather than any safety issue. The study had enrolled 61 patients and had been running since 2022, according to the federal trials register.
What Pfizer did not say may matter almost as much as the termination itself. The company declined to confirm whether all work on PF-06835375 has now been halted, and it also did not say whether it still has plans to pursue C-X-C chemokine receptor type 5, or CXCR5, as a mechanism.
What Pfizer Confirmed
A spokesperson told Fierce that the phase 2 termination was not based on safety concerns. At the time of publication, PF-06835375 still appeared on Pfizer’s website in both primary immune thrombocytopenia, or ITP, and lupus.
The lupus program appears to be further along historically than actively. A phase 1 study in lupus wrapped up in 2022, according to the trials database, but Pfizer did not use the trial termination to outline a next step for that indication either.
Why The Decision Matters
ITP is an autoimmune disorder characterized by a low platelet count. For Pfizer, ending the mid-stage study removes the clearest ongoing clinical test of PF-06835375 and shifts the story from data execution to portfolio prioritization.
Because the company framed the move as a business decision, the signal is strategic rather than clinical. That can mean capital reallocation, changing probability thresholds for internal programs, or a weaker commercial view of the indication. But the source does not specify which of those factors drove the call, so the immediate takeaway is narrower: Pfizer no longer sees enough reason to keep this particular study running.
There is also a broader readthrough for CXCR5-directed development. The target has drawn interest because CXCR5 is found in blood cancers such as diffuse large B-cell lymphoma and mantle cell lymphoma chemokine receptor, while showing little expression in normal tissue. That biology has been enough to attract developers, but not enough to guarantee durable investment when programs face competitive or financial pressure.
The recent history cited in the source is mixed. Novartis had once evaluated its B-cell-depleting antibody ianalumab in ITP, but the therapy struggled to show benefit in the clinic for that use. Outside autoimmune disease, Vincerx Pharma had planned to advance an anti-CXCR5 ADC into the clinic for B-cell malignancies, then scrapped that plan because of cash constraints.
Taken together, Pfizer’s move does not invalidate CXCR5, and the company explicitly said safety was not the issue. But it does show how quickly an asset can move from active development to strategic ambiguity when a company chooses not to explain whether a terminated study is a pause, a reset or an endpoint.
