[Tumor redifferentiation in papillary thyroid carcinoma alter retinoic acid administration].

Male patient, 73 year old, with papillary thyroid carcinoma treated by surgery, 131I and L-Tyroxine, with bone metastasis, detected by bone scintigraphy and CT scan, which negative radioiodine uptake. In order to induce tumoral redifferentiation, retinoic acid (70 mg/day) was administered for three months before 131I treatment. A radioiodine scan performed after treatment showed uptake in some of the bone metastasis. Nine months later, and due to disease progression, a second induction with retinoic acid was performed before 131I treatment. The radioiodine scan performed after treatment showed greater uptake and higher number of bone lesions than the previous scan.