Loss of MIBG positivity following induction chemotherapy with a persisting sizable residual mass lesion corresponds to absence of a significant amount of viable tumour remaining

Objectives To evaluate whether a sizable mass lesion, which has lost MIBG positivity following induction chemotherapy, still contains viable neuroblastoma.

Methods 112 children were scanned with I-123-MIBG between November 2007 and October 2011. Among them, 8 children had MIBG positive neuroblastoma that became MIBG negative after induction chemotherapy in spite of maintaining a significant size at MRI (group 1). As a control group (group 2), we included 11 children with MIBG positive primary tumour at diagnosis which maintained MIBG positivity after induction chemotherapy. We also included 4 children with MIBG negative neuroblastoma at diagnosis (group 3). The isotope scans were performed with an injected activity scaled from 400 MBq I-123-MIBG in proportion to body weight. Imaging with planar and SPECT views was obtained at 24 hours. The biopsies of 23 patients included in the study were reviewed. Following induction chemotherapy 21/23 patients had surgery and the histology was available in all cases.

Results Within group 1, 3 patients had no viable tumour remaining. The other patients showed >90% (2 patients) or >95% (3 patients) necrotic / post-chemotherapy changes. Within group 2, the 9 who had surgery demonstrated >50% viable tumour present at histology. Within group 3 no specific characteristics were identified on biopsy or excision specimen to explain the absence of MIBG uptake.

Conclusions Loss of MIBG uptake in a primary neuroblastoma after induction chemotherapy with a significantly large mass lesion on cross sectional imaging corresponds to either complete absence or minimal persistence of viable tumour. The clinical significance of this minimal amount of residual viable tumour cells is uncertain