Predicting Early Failure in Follicular Lymphoma With PET/CT Characteristics

Researchers have found several characteristics identified on PET/CT that may help to predict early clinical failure of untreated follicular lymphoma, according to a new study.

Characteristics including extranodal, splenic, and bone involvement were all predictive of early clinical failure, and may help to identify patients at high risk, wrote Frederique St. Pierre, MD, CM, of the Mayo Clinic in Rochester, Minnesota, and colleagues, in the American Journal of Hematology.

“These results provide rationale to include extranodal and spleen involvement in the PET/CT report in follicular lymphoma patients,” they wrote.

Current standard indices used for patients with indolent lymphomas do not reliably predict early therapeutic failure, according to the study. Recent studies have suggested some additional factors that may predict inferior outcome, including extranodal site involvement.

“Involvement of ≥ 2 extranodal sites by CT and bone marrow biopsy has been shown to be a univariate but not an independent adverse prognostic factor for event-free survival,” wrote St. Pierre and colleagues “These prognostic indices were derived from studies in the CT era, prior to the common use of PET imaging in staging follicular lymphoma.”

In this study, the researchers reviewed PET/CT images taken from 613 patients with untreated follicular lymphoma from 2003 to 2016. They looked at the location and number of extranodal sites, patterns of bone involvement, and splenic involvement, and assessed any relationship with event-free survival, overall survival, and early clinical failure (defined as failure to achieve event-free survival at 24 months).

About half (49%) of patients had extranodal involvement on PET/CT. The majority (77%) had only 1 site of extranodal involvement, but 19% had 2 sites, and 4% had 3 or more. The most common extranodal site was bone (68%). Splenic involvement was detected in 28% of patients.

On univariate analysis, involvement of 2 or more extranodal sites (hazard ratio [HR], 1.65; 95% CI, 1.15–2.36), the spleen (HR, 1.76; 95% CI, 1.35–2.29), soft tissue (HR, 1.73; 95% CI, 1.10–2.70), bone (HR, 1.42; 95% CI, 1.09–1.84), and pattern of bone involvement (HR, 2.16; 95% CI, 1.42–3.27) were all associated with event-free survival. Two or more extranodal sites (HR, 2.32; 95% CI, 1.31–4.11) and bone pattern (HR, 2.4; 95% CI, 1.22–4.70) were associated with overall survival.

Two or more extranodal sites of involvement, and bone, spleen, or soft tissue involvement, were all predictive of failure to achieve event-free survival at 24 months.

The researchers conducted a multivariable analysis using PRIMA-PI factors and found that the number of extranodal sites was an independent prognostic factor for inferior overall survival (HR, 2.28; P = .05).

“Although a dedicated CT of the body is also an acceptable staging modality, given our results we recommend PET/CT as the modality of choice for initial staging,” the researchers wrote. “If PET/CT extranodal/splenic involvement can be validated as predicting early clinical failure in follicular lymphoma, this will be of significant clinical benefit without adding cost to the imaging study.”