MIBG Therapy for Neuroblastoma: Precision Achieved With Dosimetry, and Concern for False Responders.

Neuroblastoma causes 15% of cancer mortality in children. High risk neuroblastoma has poor prognosis, with high relapse rate and mortality despite multimodal treatment. 123-I-meta-iodo-benzyl-guanidine (mIBG) scintigraphy is one of the current standard diagnostic procedures in neuroblastoma. mIBG can also be used therapeutically, labeled with 131-I, as a radiopharmaceutical agent, delivering targeted radiotherapy to tumoral sites. But published data of this strategy show heterogeneous results. One concern is that in most reports the infused activity is only based in body-weight, which could lead to infra or over-treatment, depending on inter-patient variability in radiation absorption. Activity adjustment by whole-body dosimetry can be used to homogeneize the treatment. Also, mIBG avid tumors may lose avidness along the treatment. As mIBG is used both for treatment and response evaluation, this could result in undetected progressions in patients with apparent complete response. We present a retrospective single-center review of neuroblastoma patients who received therapeutic 131-I-mIBG, focusing on cases with dosimetry-adjusted activity. Dosimetry allowed for a more precise delivery of radiation, reducing 81.1% of deviation from absorption target of 4 Gray (Gy), from 23.4% (±0.936 Gy) to 4.4% (± 0.176 Gy). Patients who showed partial or complete response had better and longer survival. Relapse/progression in non-responders was an early event (within 3 months from treatment). We also present one case of progression with apparent complete response due to loss of mIBG avidness, detected in our series.

Thyroid Metastasis as First Manifestation of a Colon Adenocarcinoma With KRAS Mutation: Usefulness of 18F-FDG PET/CT.

The synchronous diagnosis of a thyroid metastasis and of the primary colon adenocarcinoma that produces it is very rare, with only 5 cases reported to date, all of them treated with thyroid surgery showing a mean survival of 7 months. An ¹8F-FDG PET/CT in an asymptomatic 74-year-old woman with a thyroid cytology suggestive of malignancy but uncertain about the origin of the tumor revealed an stage IV colon adenocarcinoma with KRAS mutation and multiple metastasis (thyroid, lung, and liver). A prompt therapeutic planning with chemotherapy allowed 21 months of survival.