術後早期に脾臓に転移したsolitary fibrous tumour/haemangiopericytoma WHO grade Ⅲの1例

A Case of Meningeal Solitary Fibrous Tumour/Haemangiopericytoma WHO Grade Ⅲ Metastasized to the Spleen Shortly After Tumor Resection

Ⅰ．はじめに

　2016年に改訂された新しいWHOの脳腫瘍分類では，solitary fibrous tumour（SFT）とhaemangiopericytoma（HPC）は共通の遺伝子変異をもつことから同一の腫瘍entity（SFT/HPC）となった．組織型によりSFT phenotype，HPC phenotypeに分類され，HPC phenotypeは核分裂像の数によりgrade Ⅱ，またはgrade Ⅲ（anaplastic）に分類される⁶⁾．2004年の報告によると，HPCの局所再発や遠隔転移までの平均期間は，それぞれ47カ月，99カ月であり⁸⁾，転移までには一定の期間を要する．今回われわれは，頭蓋内発生のSFT/HPC WHO grade Ⅲに対して外科的切除術を行ったが，術後早期に再発し脾臓転移を来した1例を経験したので報告する．

　Revision of WHO guidelines in 2016 led to the classification of solitary fibrous tumours（SFTs）and haemangiopericytomas（HPCs）as a single tumor entity characterized by NAB2-STAT6 fusion. Standard-of-care treatment involves surgery, but local recurrence and distant metastasis sometimes occur. The average latency to metastasis after surgery is 99 months.

　A 38-year-old female patient presented with a complaint of headache. An 8×5×2cm lesion showing Gd-T1 enhancement was detected near the superior sagittal sinus. Pathological assessment following resection revealed proliferating, polymorphic, atypical tumor cells with distinct nucleoli in a “patternless pattern.” Cellularity was moderate to high, and mitotic figures were observed in 15/10 high power fields. Immunohistochemically, tumor cells tested positive for STAT6, and RT-PCR revealed a NAB2-STAT6 fusion gene（exons 6 and 17, respectively), supporting a diagnosis of SFT/HPC WHO grade Ⅲ. Despite postoperative radiotherapy, multiple metastases to the spleen were detected 8 months after surgery, and distal pancreatectomy with splenectomy was performed. The pathology of the splenic tumor was similar to that of the intracranial tumor. Recurrent disease in a lymph node was detected 1 month later, and local radiation therapy was administered. The patient died of cancerous peritonitis 5 months later.

　In this case, exceedingly rapid metastasis to the spleen occurred, despite the administration of vigorous treatment. Here, we review SFT/HPC incidence, treatment, and outcomes to better understand this rare malignancy.