The key finding
A 2025 meta-analysis examining 3,602 multiple myeloma patients found significant cognitive decline during the first six months of treatment across chemotherapy, stem cell transplantation, and drug therapy pathways. The standardized mean difference of 1.10 indicates a substantial effect—roughly equivalent to the difference between average and low-average cognitive performance. Interestingly, these cognitive changes appeared primarily during active treatment phases and not during maintenance therapy that extends beyond six months, suggesting the decline may be temporary rather than progressive.
What the study looked like
Researchers systematically reviewed 18 studies published between 2000 and 2024, involving 5,843 multiple myeloma patients total. Eight of these studies, comprising 3,602 participants, provided sufficient data for statistical pooling in the meta-analysis. The review included both longitudinal observational studies and randomized controlled trials that tracked patients through common treatment pathways: stem cell transplantation, chemotherapy, and targeted drug therapies. Cognitive function was measured using objective tools like the Montreal Cognitive Assessment (MoCA)—a standard screening test that evaluates memory, attention, and executive function—as well as self-reported questionnaires like the EORTC QLQ-C30, which asks patients about their perceived cognitive difficulties. The analysis specifically focused on the first six months after treatment initiation, identified as the most intensive treatment phase in multiple myeloma care.
Why researchers think this happened
The authors suggest that the intensive nature of early-phase multiple myeloma treatment—involving high-dose chemotherapy, immune system suppression during stem cell transplantation, and the biological stress of aggressive drug regimens—may directly or indirectly affect brain function. Possible mechanisms include treatment-related inflammation, chemotherapy crossing the blood-brain barrier, anemia reducing oxygen delivery to the brain, or the cumulative burden of treatment side effects like fatigue and sleep disruption. The absence of cognitive decline during maintenance therapy (which uses lower medication doses and less intensive monitoring) supports the hypothesis that treatment intensity rather than disease progression drives these changes. Previous research in other cancers has similarly documented “chemobrain,” a pattern of cognitive difficulties during active treatment that often improves afterward.
How to read this carefully
Several limitations warrant caution when interpreting these results. The bias analysis revealed potential self-selection issues—patients who volunteered for these studies may have been healthier or more cognitively intact than typical multiple myeloma patients, meaning the findings might not represent the entire patient population. More critically, most studies relied heavily on self-reported cognitive complaints rather than objective neuropsychological testing. People’s perceptions of their thinking abilities can be influenced by depression, anxiety, or treatment-related distress, which may not align with actual cognitive performance. The review did not compare patients to age- and education-matched healthy individuals, making it difficult to determine whether observed changes exceed normal aging or represent true cancer-related impairment. Finally, with only eight studies suitable for meta-analysis, more research is needed to confirm these patterns.
What this means for everyday life
If you or someone you know is beginning multiple myeloma treatment, these findings suggest it might be worth anticipating possible thinking and memory changes during the first six months—the most demanding treatment period. This doesn’t mean cognitive problems are inevitable or permanent, but being aware of the possibility can help with practical planning. You might consider strategies like keeping detailed medication lists, setting phone reminders for appointments, or asking a trusted friend to attend important medical conversations. The apparent stabilization during maintenance therapy offers reassurance that early cognitive difficulties may not worsen over time. Given that most data came from patient self-reports rather than formal testing, discussing any concerning mental fog or memory issues with your oncology team remains important—sometimes these symptoms reflect treatable factors like medication side effects, vitamin deficiencies, or sleep problems rather than direct treatment effects on the brain.