Clinical Outcomes of Low Histologic Grade Follicular Lymphoma with High Proliferation Index

Background:

Follicular lymphoma (FL) is the second most common subtype of non-Hodgkin lymphoma (NHL) accounting for ~35% of NHL and often have a clinically indolent course. PET/CT max SUV ≥10 and high proliferative index are associated with FL at high risk for transformation to aggressive lymphoma (Schöder, 2005; Rossi, 2020). A subset of patients (pts) with low histologic grade and high proliferation index (LG-HPI) have a more aggressive clinical course with inferior overall survival (OS) compared to low grade, low proliferation index (LG-LPI) FL patients (Wang, 2005). The aim of our study was to identify outcomes for patients with LG-HPI FL at our institution.

Methods:

We conducted a single center, retrospective study of FL diagnosed from 1/1/2015-1/1/2021. Demographic information, diagnoses, laboratory results, medications, pathology, and radiology reports were collected from pts' electronic medical records. Pathology specimens were de-identified and retrospectively reviewed by two pathologists. Review included comprehensive evaluation of histologic grade, proliferation index by Ki-67 percentage (Ki-67%), immunohistochemical staining, and c-MYC immunohistochemical staining. Biopsies were classified as LG-LPI if Grade 1-2 and Ki-67 was <30%, LG-HPI if Grade 1-2 and Ki-67 was ≥30%, and high grade (HG) if Grade 3A or 3B. The primary endpoint was progression free survival (PFS) defined as time from treatment until time of progression and last known follow up as determined by Kaplan-Meier method. OS was calculated from time of diagnosis to last follow up or death by Kaplan-Meier method. Comparisons were made using Log-rank model and Cox Proportional Hazards Model. Time to first treatment (TTFT) was calculated as time from diagnosis to first treatment. Receiver operating curve (ROC) was used to determine correlation between PET SUV values (defined as ≥10, or <10) and Ki-67%.

Results:

152 pts were diagnosed with FL and included for analysis. Patient characteristics are summarized in Table 1. Median age at diagnosis for all pts was 65.9 years. Sixty-three pts had LG-LPI, 61 LG-HPI, and 28 HG pts. Ten pts transformed to DLBCL (2 LG-LPI, 5 LG-HPI, 3 HG).

Treatment regimens included initial observation (n = 44), anti-CD20 therapy alone (n = 24), chemo-immunotherapy (n = 53), and other (n = 31). Median TTFT was 1.27 mo (range 0-115.2 mo). There was moderate correlation between SUV of biopsied lesion ≥10 and Ki-67 percentage (ROC Area 0.6175).

Median PFS was longer for LG-LPI compared to LG-HPI (78.6 vs 57.8 mo, p = 0.04, HR 2.37) but not between LG-HPI and HG (57.8 vs 61.3 mo respectively, p = 0.32) (Figure 1A). Median OS was not reached in any cohort with median follow up of 29.5 mo. There was no difference in OS between LG-LPI vs LG-HPI (p = 0.53) (Figure 1B). Histologic grade, proliferation index, Ann Arbor Staging, FLIPI score, PET/CT SUV intensity (max or of biopsied lesion), presence of c-Myc staining, or initial treatment regimen were not associated with median PFS or OS in either subgroup on univariate analysis.

Conclusions:

In our cohort, PFS was shorter for LG-HPI compared to LG-LPI but with a similar trajectory to that of HG FL, consistent with prior reports. No differences were seen in OS between LG-HPI and LG-LPI, and no covariates of interest including histologic grade, proliferation index, Ann Arbor Staging, FLIPI score, PET/CT SUV intensity, presence of c-Myc staining, or initial treatment regimen were associated with differences in PFS or OS. Our study is limited by a short follow up time compared to prior published cohorts (29.5 vs 98.4 mo). PET/CT SUV values of ≥10 have moderate predictive value for higher proliferative disease and can aid in identifying patients with higher proliferative disease. Longer follow up is needed to determine if LG-HPI impacts OS.

References:

1. SchöderH, et al. Intensity of 18fluorodeoxyglucose uptake in positron emission tomography distinguishes between indolent and aggressive non-Hodgkin's lymphoma. J Clin Oncol 2005;23:4643-51.

2. Rossi C, et al. Baseline SUVmaxis related to tumor cell proliferation and patient outcome in follicular lymphoma. Haematologica 2020;Online ahead of print.

3. Wang SA, et al. Low histologic grade follicular lymphoma with high proliferation index: morphologic and clinical features. Am J Surg Pathol2005;29:1490-6.

Figure 1

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Figure 1

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