## 4 Discussion  
FLs of the inguinal region are a heterogeneous group of NHLs, often characterized by unconventional features. These include a purely diffuse growth pattern, aberrant phenotypes (diffuse positivity for CD23, negativity for Bcl2 and variable expression of Bcl6), as well as unique cytogenetic and molecular changes (lack of _BCL2_ translocations, loss of 1p36, gains of 1q, mutations in _STAT6_ and _CREBBP1_) [6,7]. Our series adds to spectrum of inguinal FLs by describing a set of cases characterized by (i) deceiving clinical features, (ii) low stage at diagnosis, (iii) striking nodal necrosis, and (iv) high-grade morphology with HRS-like cells and areas of DLBCL transformation. Although limited by the small sample size, the short follow-up and lack of a control group of conventional FLs, our series presents an unusual disease pattern deserving consideration from both a clinical and pathophysiological perspective. On clinical grounds, the rapid onset and/or tenderness of the lesion, the equivocal location and ambiguous radiological features led to wrong clinical diagnoses in most cases. Only histological assessment revealed the true nature of the disease, despite large (even  
Figure 1: **Morphological features of necrotizing FL of the inguinal region. ** (**A–C**) Low-power magnification disclosed nodal effacement by large areas of ischemic necrosis with peripheral lymphoid aggregates **(A)**. The latter had either a nodular **(B)** or diffuse **(C)** growth pattern. **(D–F)** At higher magnification, nodular areas featured a mixture of centrocytes and centroblasts **(D)**; diffuse areas were instead composed mainly of large blasts **(E)** with scattered CD30-positive, HRS-like cells **(F)**. ( Hematoxylin and Eosin stain; original magnification, 1.25\(\times\), 5\(\times\), 20\(\times\) and 40\(\times\)). Figure 2: **Phenotype of necrotizing FL of the inguinal region. ** Immunohistochemistryal analysis showed diffuse positivity for CD20 with rare CD30-positive, HRS-like cells (insert). Neoplastic B cells were mostly positive for Bcl6 and CD10 with variable Bcl2 and CD23 expressions. CD23 also highlighted follicular dendritic cell meshworks in nodular areas (insert). The ki67 proliferation index was high in both nodular and diffuse areas, with consistent negativity for EBER. (Peroxidase stains; original magnification, 20\(\times\) and 40\(\times\)). massive) necrotic areas impinging on microscopic evaluation. Even with such alarming features, response to therapy was excellent and follow-up data suggested a favorable clinical course. Extensive necrosis is rarely observed in B-cell lymphomas, usually being associated with highly aggressive entities [8; 9; 10; 11], Hodgkin lymphoma [12] and EBV-positive lymphoproliferative disorders [13; 14]. When abundant, necrosis may even obscure the lymphoid nature of the process, suggesting alternative diagnoses, such as nodal metastasis by solid tumors, non-specific ischemic lesions, and necrotizing lymphadenitis secondary to pyogenic, mycobacterial or fungal infections. In our cases, all of these diagnoses were excluded by careful morphological and immunohistochemical evaluations. In particular, the diagnosis of FL was supported by the presence of residual follicles with atypical GC B cells and preserved dendritic cell meshworks. In line with prior studies on inguinal FL [6], Bcl2 was heterogeneously expressed, with one case being completely negative for this marker. Moreover, \(BCL2\) translocations were lacking in all tested cases (another finding typical of subsets of inguinal and grade 3B FLs) [6; 15]. This unusual phenotype complicates the recognition of FL and may suggest the alternative diagnosis of necrotizing lymphadenitis with reactive follicular hyperplasia.