[Clinicopathological Characteristics of Follicular Lymphoma with a Predominantly Diffuse Growth Pattern]

To investigate the clinicopathological features, diagnosis, differential diagnosis, treatment, and prognosis of a patient with follicular lymphoma with predominantly diffuse growth pattern (DFL), in order to enhance understanding of this rare lymphoma variant.

Clinical and pathological data of one patient with DFL were collected. A retrospective analysis was conducted on the patient's clinical manifestations, pathological morphological features, immunophenotype, molecular genetic changes, treatment, and follow-up outcomes. Relevant literature was also reviewed.

The patient was a 43-year-old female, presenting with a right inguinal area of more than four years' duration. Gross pathological examination revealed a single lymph node measuring 4.0 cm×3.0 cm×2.0 cm, with a gray-white, solid, and soft cut surface. Microscopic evaluation demonstrated architectural effacement and diffuse proliferation with focal residual indistinct follicular structures. Under high magnification, the tumor cells were predominantly centrocytes with a few scattered centroblasts in a heterogeneous background. Immunohistochemistry showed positive expression of CD10, BCL-6, and CD23 in tumor cells, but negative for BCL-2. STAT6 showed weak staining in <1% of tumor cells and was interpreted as negative. Fluorescence in situ hybridization (FISH) showed neither 1p36 deletion nor BCL2 rearrangement. Clonality analysis demonstrated clonal rearrangement of immunoglobulin genes, while T-cell receptor (TCR) gene rearrangement showed a polyclonal pattern. The patient underwent radiotherapy (24 Gy/12 fractions) to the right inguinal area, and has achieved complete remission to date.

DFL is a rare subtype of follicular lymphoma with unique clinicopathological features and molecular genetic alterations, which may lead to diagnostic confusion with T-cell lymphomas. Accurate recognition of this subtype helps avoid misdiagnosis and inappropriate treatment. DFL is generally characterized by low histological grade, early clinical stage, and a favorable prognosis.