PET/CT Can Assess Early Treatment Response in Newly Diagnosed MM

In patients with newly diagnosed multiple myeloma (MM), a negative positron emission tomography (PET)/CT exam at 6 months is associated with improved survival, according to a study published in Blood Advances.

Typically, biochemical assessment of disease activity is used to monitor treatment response, 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 examination at baseline and at approximately 6 months (range, 2-9 months) after diagnosis.

Negative PET/CT (PET/CT [–]) per the International Myeloma Working Group (IMWG) “was defined as the disappearance of every area of increased FDG uptake found at baseline, or a decrease in uptake to less than mediastinal blood pool activity, or a decrease in metabolic activity to less than that of surrounding normal tissue.” Patients with residual disease were categorized as “progressed” if they had new areas of increased FDG metabolism or “positive” (PET/CT [+]) if lesions had not disappeared entirely.

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

The median age of the patients in the PET/CT (–) cohort was 59.7 years compared with 61.8 years for the positive cohort. Overall, the majority (90.3%) of patients were White. There was a higher proportion of males in the negative cohort (72.0% vs 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 (95% CI, 63.1-119.1). Overall, 25.1% of patients (20.0% in PET/CT [–] vs 26.9% in PET/CT [+]) had extramedullary disease, which is a known adverse prognostic finding in MM, on their initial evaluation. Lenalidomide, bortezomib, and dexamethasone was the most common regime used for induction among the entire cohort (28.7%).

At the 6-month mark, only 25.6% of patients were PET/CT (–). The rest of the patients had detectable disease and 30 patients had signs of progression.

The authors found:

• At 6 months, median TTNT for PET/CT (–) was 55.2 months compared with 25.1 months for PET/CT (+) and 7 months for PET/CT with progression (P < .0001)
• Patients with PET/CT (–) results did not reach median OS compared with 72 months for PET/CT (+) and 27.7 months for PET/CT with progression
• 27.7% of patients attained a complete response (CR) at their second PET/CT
  • 24 patients were PET/CT (–) and 30 were PET/CT (+)
  • Compared with patients who reached a CR and were PET/CT (+), patients who had a CR and were PET/CT (–) had prolonged TTNT (58.9 vs 39.2 months; P = .27) and OS (unreached vs 72 months; P = .01)

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

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

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

Reference

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