Results of a recent Swiss study show that multiple myeloma patients who have a high level of stem cells in the blood prior to stem cell transplantation have longer progression-free and overall survival times than patients who have fewer stem cells.

Based on these findings, the study authors recommended that physicians consider the number of stem cells in the blood of myeloma patients when determining their prognoses and developing appropriate post-transplant therapies.

“We feel that [the level of stem cells] is first a novel prognostic marker. Second, we think that it may have the potential to help identify patients who might benefit from specific post-consolidation or maintenance treatment,” said Dr. Thomas Pabst of the University of Berne in Switzerland and one of the study authors.

Dr. Pabst and his colleagues acknowledged, however, that the reason for improved outcomes among myeloma patients with high levels of stem cells is still unknown.

Dr. William Bensinger of the Fred Hutchinson Cancer Center in Seattle, who was not involved in the study, commented that it is too early to alter myeloma therapy based on these findings.

“These results are potentially important, but it is too early to say. Until we understand more about why this occurs, it is not possible to say how this might affect treatment,” Dr. Bensinger told The Myeloma Beacon.

Dr. Jayesh Mehta of the Northwestern University Feinberg School of Medicine in Chicago, who was also not involved in the study, added that the results of the study would be more reliable if other patient risk factors, such as chromosomal abnormalities, had been taken into account.

A common approach to treating newly diagnosed myeloma patients under the age of 65 begins with novel agent-based initial therapy followed by high-dose chemotherapy and autologous stem cell transplantation.

Treatment with high-dose chemotherapy followed by autologous stem cell transplantation is a common therapy for newly diagnosed myeloma patients up to 65 years of age.  During the transplant procedure, a patient’s stem cells are collected prior to high-dose chemotherapy and then later re-infused into the patient to replace the cells that were destroyed during chemotherapy.

Most stem cells originate in the bone marrow. To facilitate the stem cell collection process, patients frequently receive treatments, such as granulocyte colony-stimulating factor (G-CSF) or Mozobil (plerixafor), to mobilize stem cells from the bone marrow into the blood.

Previous studies have indicated that patients with lymphoid cell cancers who had high numbers of stem cells in their blood experienced longer survival after receiving a stem cell transplant than patients who had fewer numbers of stem cells.

In this study, the Swiss researchers sought to determine whether multiple myeloma patients with a high number of stem cells in the blood also experience improved survival outcomes after receiving a stem cell transplant.

The study included 158 myeloma patients with a median age of 56 years. All patients had received an autologous stem cell transplant between 2001 and 2010. Prior to the transplant, all patients received G-CSF for stem cell mobilization followed by either high-dose cyclophosphamide (Cytoxan) or vinorelbine (Navelbine).

Patients were divided into two groups based on the number of stem cells in their blood on the day of stem cell collection. Patients who had over 100,000 stem cells/ml were categorized as super mobilizers (44 percent), while those who had under 100,000 stem cells/ml were categorized as normal mobilizers (56 percent).

Super mobilizers received, on average, a larger number of stem cells during transplantation than normal mobilizers (5,270,000 stem cells versus 3,560,000 stem cells).

The researchers found that fewer super mobilizers experienced disease progression after their stem cell transplant than normal mobilizers (17 percent versus 27 percent). In addition, super mobilizers had a longer median time to disease progression than normal mobilizers (46 months versus 33 months).

The median overall survival time of all patients was 72 months. Normal mobilizers had a median overall survival time of 50 months, while super mobilizers did not yet reach the median overall survival when the study was completed.

After a median follow-up of 32 months, 27 percent of patients have died. Of these patients, 8 percent were super mobilizers and 19 percent were normal mobilizers.

According to the study authors, super mobilizers achieved better outcomes than normal mobilizers independent of the type of chemotherapy, disease stage, or the number of stem cells they received during their stem cell transplant.

Dr. Pabst and his team plan to conduct additional studies to further investigate the role of stem cell levels in the treatment of myeloma.

“We are in the process of designing a study which uses [the level of stem cells] for stratification of patients allocated to less versus more post-consolidation or maintenance treatment,” said Dr. Pabst.

“In addition, we would love to test our findings in a much larger cohort of myeloma patients,” he added.

For more information, please see the article in the British Journal Of Cancer (abstract).