This study aims to investigate the clinicopathological features of in situ follicular neoplasm (ISFN) in Japan. ISFN is a rare condition formerly considered as an early precursor of follicular lymphoma (FL). This is a first original report of ISFN from Asian country. We reviewed 19 biopsy samples of ISFN. ISFNs were categorized into two groups: (1) ISFN, consisting of ISFN with strong positivity for BCL-2 immunohistochemical staining (IHC), and obvious translocation of BCL-2; and (2) ISFN-like FL, featuring cases without obvious translocation but having morphological features and characteristic IHC findings of ISFN. As control, we adopted obvious FL. For some cases showing coexisting ISFN and FL lesions in the same lymph node, we could conduct further clonality analysis for each lesion. Nine of the 19 cases of ISFN coexisted with FL or had a history of overt B- or T-cell lymphoma including FL. Statistical comparison among ISFN-like FL and FL showed no significant differences in pathological features. Molecular analysis suggested that ISFN lesion and FL lesion in the same lymph node each have a different clonality. ISFN coexists or associates with other overt lymphomas frequently.

中文翻译：

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日本原位滤泡性肿瘤的临床病理特征及其与滤泡性淋巴瘤的关系。

这项研究旨在调查日本原位滤泡性肿瘤（ISFN）的临床病理特征。ISFN是一种罕见病，以前被认为是滤泡性淋巴瘤（FL）的早期先兆。这是亚洲国家ISFN的第一份原始报告。我们审查了19例ISFN的活检样本。ISFN分为两类：（1）ISFN，由对BCL-2免疫组织化学染色（IHC）阳性强且BCL-2明显易位的ISFN组成；（2）ISFN样FL，特征是病例无明显易位，但具有ISFN的形态特征和IHC特征。作为对照，我们采用了明显的FL。对于某些在同一淋巴结中同时存在ISFN和FL病变的病例，我们可以对每个病变进行进一步的克隆性分析。19例ISFN病例中有9例与FL共存或有明显的B细胞或T细胞淋巴瘤包括FL的病史。ISFN样FL和FL之间的统计比较表明，病理特征无明显差异。分子分析表明，同一淋巴结中的ISFN病变和FL病变各自具有不同的克隆性。ISFN经常与其他明显的淋巴瘤共存或伴发。