An extra shot helped 9 in 10 cancer patients bank stem cells for a transplant

Before some cancer treatments, patients spend hours hooked up to a machine that sorts their blood. It picks out stem cells, young cells that can grow into new blood cells, and sends the rest of the blood back. Many patients have to come back for more than one of these long sessions to collect enough [1].

A trial of 122 adults with multiple myeloma, a cancer of the bone marrow, tested an extra shot meant to make that easier. With it, 92.5 percent collected enough cells in two sessions or fewer. That is about 9 in 10. With a look alike shot with no medicine in it, only 26.2 percent did, about 1 in 4 [1].

One thing is worth saying early. This trial compared the new shot with a fake shot, not with the older drug doctors already use for this job. When a later, smaller study did compare the two, it found no gain [1][2].

The shot is called motixafortide. The trial, known as GENESIS, was led by Zachary Crees of Washington University School of Medicine in St. Louis. It was published in the journal Nature Medicine in 2023. Six of its authors worked for BioLineRx, the company that makes the shot [1][3].

Why do these patients need their stem cells at all? Many people with this cancer get a transplant of their own cells. Doctors collect and save the cells first. Then the patient gets very strong chemotherapy, cancer medicine that also wipes out the bone marrow, the soft middle of bones where blood is made. The saved cells are then put back so the marrow can grow again [1].

Stem cells mostly stay inside the bone marrow, so doctors coax them out into the blood with several days of a shot called a growth factor. Then the sorting machine collects them, a process called apheresis. Teams aim for about six million of one kind of stem cell for each kilogram the patient weighs. The researchers put the problem this way:

However, many individuals are unable to collect optimal CD34+ hematopoietic stem and progenitor cell (HSPC) numbers with granulocyte colony-stimulating factor (G-CSF) mobilization.

Crees and colleagues, Nature Medicine, 2023 [1]

In plain words, many patients cannot collect enough stem cells with the growth factor alone. The new medicine is meant to help. It is a peptide, a short chain of small building blocks called amino acids, joined into a ring. It blocks a part of the cell called CXCR4, which works like a rope holding stem cells inside the bone marrow. With that rope let go, more stem cells drift out into the blood [1].

How was the trial run?

The trial ran at 18 hospitals in five countries, and every patient got the growth factor. Chance decided, like a coin flip, who also got the new medicine and who got the fake shot. Two people got the medicine for every one on the fake shot, and neither the patients nor the doctors knew who got what [1].

The gap was even bigger in a single session. On the medicine, 88.8 percent reached the goal in one try, against 9.5 percent on the fake shot. That is almost 9 in 10, against about 1 in 10. The most common side effects were mild or medium reactions where the shot went in, such as pain in half the patients [1].

The United States approved the shot on 11 September 2023, for use with the growth factor in this exact job [3]. But the trial counted cells, not people's health. That matters, since a patient who reaches the goal in one session does not have to come back. Still, the trial did not measure how the transplant went, how long the cancer stayed away, or how long anyone lived [1].

What happened when it was compared with the older drug?

In 2026, a team at the Dana-Farber Cancer Institute in Boston published the first direct comparison with plerixafor, the older drug doctors use when the growth factor is not enough. It looked at 30 patients who got the new shot and 30 similar patients who got the older drug. Both drugs pulled out about the same number of stem cells, and 27 patients in each group reached the goal in one day. The team concluded:

In this first real-world comparison, use of motixafortide was feasible but not superior to plerixafor for MM mobilization.

Close and colleagues, Transfusion, 2026 [2]

In plain words, the new shot could be used, but it did no better. Bad reactions that needed care, where the shot went in and across the body, were much more common with it. Patients also needed medicine beforehand and close watching after. The hospital kept the older drug as its usual choice and saved the new one for some patients only [2].

That study is weaker than the big trial. It had only 60 patients at one hospital, and one group came from past records rather than being picked by chance. So it cannot cancel out the big trial, but it is the only direct comparison so far [2].

So what does this work show? The new shot reliably moves stem cells into the blood, far better than a fake shot does. It does not show that it beats the older drug, or that patients ended up healthier. A trial that picks patients by chance for the two drugs, and follows them after the transplant, would answer that [1][2][3].