Indolent Follicular Lymphoma with “Hot” PET: A Clinic–Radiologic Mismatch That Challenges Early Treatment vs Watchful Waiting

Follicular lymphoma (FL) grade 1–2 typically behaves indolently and is often managed with watchful waiting when tumor burden is low. However, moderately high FDG uptake on PET-CT may suggest biological heterogeneity or incipient transformation despite low-grade histology, creating a management dilemma. We report a patient with biopsy-proven FL grade 1–2 and unexpectedly “hot” PET signals, illustrating decision points between immediate therapy and surveillance.

Single-patient case report. We reviewed clinical data, laboratory tests, excisional lymph-node histology with immunohistochemistry (IHC), bone marrow (BM) evaluation, and whole-body PET-CT at diagnosis. Management decisions were based on symptoms, tumor burden, and longitudinal imaging.

A 53-year-old woman presented with a painless, mobile left axillary mass detected 2 months earlier. She denied fever, drenching night sweats, or weight loss. Physical exam revealed a ∼3 cm left axillary node; no hepatosplenomegaly or other palpable lymphadenopathy.

PET-CT demonstrated a 30 × 22 mm left axillary node with SUVmax 9.12, additional mediastinal paraaortic/aortopulmonary nodes (SUVmax 5.89), and tiny bilateral apical lung nodules with low uptake. The liver contained a 15 × 12 mm hypodense lesion with faint FDG avidity and mild hepatomegaly; spleen and adrenals were normal; bone involvement was absent.

Excisional node biopsy showed classical FL, grade 1–2. IHC: CD20+, CD23+, CD5–, Cyclin D1–; Ki-67 ≈10%. BM aspirate/biopsy exhibited normal hematopoiesis with no lymphoma infiltration (reticulin 0/4; amyloid negative). Baseline blood counts and biochemistry were within reference limits except for a mildly elevated LDH.

Composite staging favored advanced-stage (IIIA–IIIB) FL owing to mediastinal involvement and hepatomegaly, yet clinical tumor burden was low: solitary bulky node absent, no B symptoms, preserved counts, and no organ compromise.

Given the discrepancy—indolent histology with relatively high axillary SUV—management options were discussed. Because transformation was not proven (low Ki-67, no high-grade features on biopsy, and no PET focus >10 with structural suspicion elsewhere), we selected watchful waiting with close clinical and PET/CT surveillance, reserving therapy for symptomatic progression, GELF high-tumor-burden criteria, rising SUVs or node growth, or any histologic evidence of transformation (repeat biopsy triggered by interval changes). Single-agent rituximab or R-based chemoimmunotherapy would be considered if progression occurs.

This case highlights a clinic–radiologic mismatch: low-grade FL with SUVmax ∼9 in the index node. While high SUVs in FL can raise concern for transformation, histology and low proliferation argued against immediate cytotoxic therapy. In asymptomatic, low-burden FL, watch-and-wait remains appropriate, provided that surveillance is disciplined and re-biopsy is performed for PET-dominant changes or clinical progression. Educationally, the case underscores the limits of relying on SUV alone, the centrality of tissue confirmation, and the value of individualized triggers for treatment versus observation.

In FL grade 1–2 with “hot” PET but low clinical burden, structured watchful waiting with planned re-biopsy on interval change can safely balance overtreatment risks against the need to detect transformation early.