A Clinicopathologic Evaluation of Follicular Lymphoma Grade 3A Versus Grade 3B Reveals No Survival Differences

Archives of Pathology & Laboratory Medicine, Aug 2004 by Hsi, Eric D, Mirza, Imran, Lozanski, Gerard, Hill, John, Et al

* Context.-The World Health Organization classification recommends categorizing grade 3 follicular lymphomas based on the presence of centrocytes (grade 3A) or of sheets of centroblasts (grade 3B). The clinical significance of this practice is not known.

Objective.-To determine whether grade 3 follicular lymphoma subtype is associated with prognosis.

Design.-Multi-institutional retrospective case series.

Main Outcome Measure.-Overall survival.

Results.-Forty-five cases of grade 3 follicular lymphoma without diffuse large B-cell lymphoma were studied (35 cases of grade 3A, 10 cases of grade 3B) from 21 men and 24 women (median age, 67 years; mean age, 63.8 years; range, 26-86 years). Follow-up information from the time of diagnosis was available in all patients, with a median follow-up time of 24 months (mean, 34 months; range, 2-115 months). Treatment information was available in 40 patients. There was no difference in age (P = .45, Wilcoxon test) or stage (P = .76, Fisher exact test) between patients with follicular lymphoma of grade 3A or grade 3B. Furthermore, the Cochran-Armitage test for trends showed no evidence that the proportion of patients with follicular lymphoma grade 3A or 3B increased or decreased with increasing stage at presentation. Kaplan-Meier analysis showed a median overall survival of 44 months from the time grade 3 follicular lymphoma was diagnosed, with no significant difference between cases diagnosed as grade 3A or grade 3B (P = .14, log-rank test). Univariable Cox proportional hazards modeling showed no evidence that an anthracycline-containing chemotherapy regimen or history of lower grade follicular lymphoma affected overall survival.

Conclusions.-In this retrospective series, subclassification of grade 3 follicular lymphoma into type 3A and 3B categories had limited clinical and prognostic significance. However, the study was limited by lack of statistical power. Since morphology often provides clues for progress in defining biologic differences, subtyping may still be useful, particularly in the setting of prospective clinical studies.

(Arch Pathol Lab Med. 2004;128:863-868)

Follicular lymphoma (FL) represents 25% of all adult non-Hodgkin lymphomas in the Western world.1 It is a clinically indolent lymphoma that generally presents at high clinical stage, and the expected median survival is approximately 8 to 10 years, a figure that has not changed substantially in the last 30 years.2 The putative cell of origin is the germinal center B cell. Central to the pathogenesis of this lymphoma is t(14;18)(q32;q21).1 This translocation results in overexpression of the bcl-2 gene, causing resistance to apoptosis.4 Histologically, FL is a neoplasm of centrocytes and centroblasts showing at least partial follicular architecture. The tumor cells express monotypic surface immunoglobulin, B-cell antigens CD9 19 and CD20, CDlO, and Bcl-6. The proportion of centrocytes and centroblasts can vary considerably, and over the years cytologie grading has been shown to be of prognostic and therapeutic significance. For example, the International Working Formulation (IWF) showed outcome differences based on the proportion of large cells present in the follicles. Follicular large cell lymphoma was placed into the intermediate-grade category, along with diffuse large cell lymphoma, whereas follicular small cleaved and follicular mixed small cleaved and large cell lymphomas were considered low-grade lymphomas.5

Grading of FL has, however, been fraught with irreproducibility problems. The system of Mann and Berard was shown to be reproducible and was recommended by the International Lymphoma Study Group in the Revised European-American Classification of Lymphoid Neoplasms.6,7 In this system, FL grades are assigned according to the number of large cells (centroblasts) in 10 different representative neoplastic follicles not selected for those with the most numerous large cells. The count is based on a high-power field (HPF) of 0.959 mm^sup 2^, which is defined as a field resulting from use of an ocular with an 18-mm^sup 2^ field of view at �lO magnification and �40 objective (with appropriate correction factors to compensate if different field oculars are used). Follicular lymphomas with O to 5 centroblasts per HPF are classified as a grade 1, with 6 to 15 centroblasts per HPF as grade 2, and with more than 15 centroblasts per HPF as grade 3. The recent World Health Organization (WHO) classification further proposes to subclassify grade 3 into grades 3A and 3B, based on the presence or absence of centrocytes in the neoplastic follicles.8

It is uncertain whether there is any biologic or clinical utility to subdividing grade 3 FLs, as suggested by the WHO classification. Therefore, we decided to retrospectively evaluate the importance of morphology-based subclassification of FL grade 3 into FL grades 3A and 3B with respect to overall survival in a series of 45 cases of grade 3FL.

MATERIALS AND METHODS

Excisional biopsy specimens of grade 3 FL without a diffuse large B-cell component were retrieved from the pathology files of the Cleveland Clinic Foundation (Cleveland, Ohio; n = 21) and Cross Cancer Center (Edmonton, Alberta; n = 24). The cases were categorized as FL grade 3A or 3B according to WHO criteria after a panel of 3 hematopathologists reached consensus. Observers were blinded as to outcome. Olympus BX-40 or BH-2 microscopes with �40 objectives and �lO oculars (20-mm field of view) were used, with correction for expanded field of view in centroblast counting when necessary. Follicular lymphoma grade 3B follicles were essentially composed of sheets of centroblasts, while FL grade 3A had remaining cleaved cells present, interspersed among the centroblasts. Only cases showing pure follicular pattern on hematoxylin-eosin-stained sections without diffuse areas were included in this study. Clinical data, such as demographics, Ann Arbor stage at presentation, history of previous diagnosis of lower grade FL, and use of anthracycline in treatment, and follow-up data were evaluated by chart review.