Preservation of follicle mantle in follicular lymphoma

Follicular lymphoma (FL) is a low-grade lymphoma with a follicular growth pattern, a peculiar immunophenotype, and a characteristic t(14;18) chromosomal translocation involving the bcl2 gene locus in the majority of cases. The diagnosis of a full-blown FL is usually easily established. However, those cases presenting only partial infiltration of the lymph node in association with reactive follicular hyperplasia may be challenging and Jaffe et al. have proposed the term ‘‘in situ localization of follicular lymphoma’’ for such cases [1,2]. Despite the low frequency of true in situ FL, a significant number of FL show preservation of the mantle zone in otherwise completely infiltrated lymph nodes. The biological significance of this finding is unclear. Cells of the follicle mantel zone (FM) are CD20 positive B-cells with co-expression of IgD. Moreover, CD23 is expressed on a subset of these cells. Since we and others have recently analyzed the expression of CD23 in FL cells [3,4] which proved to be correlated to the localization of the lymph node [3], we decided to systematically study the prevalence of preserved mantle zones in FL in association to some clinical characteristics. In total 186 FL, comprising 64 samples from inguinal lymph nodes and 122 samples from other regions, were analyzed by morphology and immunohistochemistry. The histomorphologic features of the lymph nodes were assessed on haematoxylin and eosin-, periodic acid-Schiff-, Giemsaand Gomoristained sections of formalin-fixed, paraffinembedded tissue. Immunohistochemical stainings were performed according to a standard three-step immunoperoxidase technique with diaminobenzidine as chromogen. The following antibodies were used: CD20, bcl-2, Mib-1, IgD (Dako, Denmark), CD23, and CD10 (Novocastra, Newcastle, UK). In this study, preservation of FM was defined as a rim of IgD positive cells around neoplastic follicles, encircling at least 25% of a follicle. IgD stainings were evaluated as percentage of neoplastic follicles with preserved FM as defined above. The IgD staining was not evaluable in four cases, leaving 182 cases for the analysis. One hundred cases (55%) did not show any preserved FM, whereas in 82 cases (45%) a very variable number of preserved FM could be demonstrated. The number of neoplastic follicles with FM ranged from as low as 5% to as much as 100%. In 22 cases (12%), the mantle zones were present around the majority ( 50%) of neoplastic follicles, whereas in the remaining 60 cases (33%) only a minority of follicles showed preservation of FM (mean 16%+ 11%). The results are summarized in Table I. When comparing CD23 positive and negative cases, there was a slightly higher number of cases with FM preservation in the CD23 negative group (46% vs. 36%). However, the difference was not significant (U-test, p1⁄4 0.16). With respect to different localization (inguinal lymph node vs. other), the frequency of preserved FM was very similar (46% and 45%). The same holds true for lowand high-grade tumours (46% and 43%). Preservation of FM was slightly more often in patients under the age of 60 (50% vs. 42%) as well as in male patients (51 vs. 40%).