PET/CT can assess early response to treatment in newly diagnosed MM

Negative positron emission tomography/CT scan 6 months after induction therapy in patients with newly diagnosed multiple myeloma (MM) is associated with prolonged time to next therapy and overall survival.

According to a study published in Blood Advances.

Typically, biochemical assessment of disease activity is used to monitor response to treatment, and PET/CT results can add “significant prognostic value,” according to the authors.

The retrospective cohort study included 195 patients with newly diagnosed MM who were seen at Mayo Clinic between 2004 and 2020. All patients had an 18F-fluorodeoxyglucose (FDG) PET/CT scan at baseline and around 6 months (range, 2-9 months) after diagnosis.

PET/CT negative (PET/CT [–]) according to the International Myeloma Working Group (IMWG) “was defined as the disappearance of each area of ​​increased FDG uptake found at baseline, or decreased uptake unless blood pool activity mediastinal, or decreased metabolic activity less than that of surrounding normal tissues.Patients with residual disease were classified as “progressive” if they had new areas of increased FDG metabolism or “positive” (PET /CT [+]) if the lesions had not entirely disappeared.

The researchers collected baseline clinical characteristics for the entire cohort in order to make comparisons between the PET/CT (–) and PET/CT (+) subgroups. Endpoints were time to next treatment (TTNT) and overall survival (OS).

The median age of patients in the PET/CT (–) cohort was 59.7 years versus 61.8 years for the positive cohort. Overall, the majority (90.3%) of patients were Caucasian. There was a higher proportion of males in the negative cohort (72.0% versus 66.9%).

The median follow-up for the entire cohort was 80.6 months, the median TTNT was 24.6 months (95% CI, 20.4-29.1), and the median OS was 79 months (CI at 95%, 63.1-119.1). In total, 25.1% of patients (20.0% in PET/CT [–] vs 26.9% in PET/CT [+]) had extramedullary disease, which is a known poor prognostic outcome in MM, at their initial evaluation. Lenalidomide, bortezomib and dexamethasone was the most commonly used regimen for induction among the entire cohort (28.7%).

After 6 months, only 25.6% of patients were PET/CT (–). The rest of the patients had detectable disease and 30 patients showed signs of progression.

The authors found:

  • At 6 months, the median TTNT for PET/CT (–) was 55.2 months versus 25.1 months for PET/CT (+) and 7 months for PET/CT with progression (P
  • Patients with PET/CT results (–) did not achieve median OS versus 72 months for PET/CT (+) and 27.7 months for PET/CT with progression
  • 27.7% of patients achieved a complete response (CR) on their second PET/CT
    • 24 patients were PET/CT (–) and 30 were PET/CT (+)
    • Compared to patients who achieved CR and were PET/CT (+), patients who had CR and were PET/CT (–) had a prolonged TTNT (58.9 vs 39.2 months ; P = 0.27) and OS (not reached vs 72 months; P = .01)

Overall, the results showed that PET/CT status (–) at 6 months after induction therapy was associated with significantly prolonged median TTNT and OS compared to patients who were PET/CT (+ ), noted the authors.

Among the limitations noted were the nature of the study design and the possibility of selection bias, with patients receiving diagnostic and post-treatment PET/CT being part of a higher risk subgroup.

“Our study highlights the role of PET/CT in the evaluation of patients with MM in the post-treatment setting,” the authors concluded. “We have shown that PET/CT can consistently improve the definition of biochemical responses, as defined by the IMWG, especially for patients with skeletal involvement at the time of diagnosis.”

Reference

Charalampous C, Goel U, Broski SM, et al. Usefulness of PET/CT to assess early response to treatment in patients with newly diagnosed multiple myeloma. Adv of blood. 2022;6(9):2763-2772. doi:10.1182/bloodadvances.2022007052

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