Histological features of primary tumors after induction or high-dose chemotherapy in high-risk neuroblastoma Tomoro HishikiHiroshi HorieYasuyuki HigashimotoKatsumi YotsumotoShugo Komatsu • Yuri OkimotoHarumi KakudaYuichi TaneyamaTakeshi SaitoKeita TeruiTetsuya Mitsunaga • Mitsuyuki NakataHidemasa OchiaiMoeko HinoKumiko AndoHideo YoshidaJun Iwai

Purpose In the recent years in Japan, an increasing number of patients with neuroblastoma (NB) are being treated by the ‘‘delayed local treatment (DL)’’ policy, undergoing surgery after the completion of high-dose chemotherapy with hematopoietic stem cell rescue (HDC). We reviewed the histopathological findings of second-look operations, including those of patients treated with DL. Patients From 1998 to 2013, 26 patients with high-risk NB underwent radical operation following chemotherapy. Surgery was performed after induction chemotherapyin 17 cases (standard; STD), whereas 9 cases completed induction chemotherapyand HDC before undergoing tumor resection (DL). The amount of necrosis and the degree of differentiation within the post-treatment tumor were assessed. Results Eighty-eight percent of the tumors showed necrosis in more than 1/3 of the specimen. Two DL cases showed complete disappearance of viable tumor cells. Amount of necrosis did not affect the prognosis of the patient. Tumors with immature, poorly differentiated phenotypes showed an extremely aggressive thereafter. Though not statistically proven, 123 I-MIBG (metaiodobenzylguanidine) uptake may be correlated with the amount of viable cells remaining within the tumor, but not with the degree of differentiation. Conclusions Our results support the previous reports advocating that tumors that sustain unfavorable histology after chemotherapy behave aggressively thereafter.