Histology of Follicular Lymphoma (FL)

FL, when viewed under the microscope often consists mostly of small cells called centrocytes and some larger centroblasts.1,2

  • Centrocytes typically have cleaved nuclei and appear with an abnormal, stretched shape1-3
  • Centroblasts are larger cells that may have round (non-cleaved) or cleaved nuclei1,3
  • They often have more open chromatin, giving a lighter appearance to the nucleus3
  • The number of centroblasts per high-power field (HPF) may be counted and used to estimate the aggressiveness of the disease1

Histological appearance of follicular lymphoma

Neoplastic follicles have vague borders and minimal or absent mantle zones. In addition, they have typically lost normal polarity, resulting in a more homogeneous appearance without clear dark and light zones.1,2 FL often appears as a collection of back-to-back neoplastic B cell follicles. These may be similar in size and shape, or may be a heterogeneous collection of small and large follicles.1,2

The histological appearance of FL can sometimes be similar to other types of B cell lymphomas, and so further molecular testing and immunophenotyping should be conducted to confirm the diagnosis.1

FL Grading

In follicular lymphoma, the proportion of centroblasts varies from case to case.4,5 Tumor grading defines the clinical aggressiveness of FL, which increases with the number of centroblasts.4

  • GRADE 1: 0 to 5 centroblasts/HPF5
  • GRADE 2: 6 to 15 centroblasts/HPF5
  • GRADE 3: >15 centroblasts/HPF5
    • 3a: Centrocytes are present
    • 3b: Solid sheet of centroblasts

Histology of follicular lymphoma6

HPF, high-power field; WHO, World Health Organization.

HPF, high-power field; WHO, World Health Organization.

References: 1. Choi SM, et al. Arch Pathol Lab Med. 2018;142:1330–1340. 2. Takata K, et al. J Clin Exp Hematop. 2014;54(1):3-9. 3. UMDNJ. Follicular Lymphomas. http://pleiad.umdnj.edu/~dweiss/follicular/follicular.html. Accessed January 25, 2019. 4. Wahlin BE, Yri OE, Kimby E, et al. Clinical significance of the WHO grades of follicular lymphoma in a population-based cohort of 505 patients with long follow-up times. Br J Haematol. 2011;156:225–233. 5. Campo E, Swerdlow SH, Harris NL, Pileri S, Stein H, Jaffe ES. The 2008 WHO classification of lymphoid neoplasms and beyond: evolving concepts and practical applications. Blood. 2011;117(19):5019-5032. 6. Oncolex Oncology Encyclopedia. Follicular lymphomas grades 1, 2, and 3A. http://oncolex.org/lymphoma/diagnoses/non-hodgkin-lymphoma/diagnoses/b-celllymphomas/background/follicularlymphomasgrades1and2and3a. Accessed September 13, 2019.