The early detection of all tumor sites in patients with medullary thyroid carcinoma (MTC) before primary surgery is important, because MTC tends to metastasize to regional lymph nodes of the neck and mediastinum early during the course of the disease.
Methods: In an approach to localize the primary tumor sites and to detect additional tumor involvement, we have performed in 22 patients with MTC either 99mTc(V)-dimercaptosuccinic acid (DMSA) and/or 111In-diethylenetriamine pentaacetic acid-D-Phe-1-octreotide scintigraphy.
Results: Indium-111-octreotide (150-200 MBq) identified the primary tumor in 10 of 14 patients (71%), whereas the primary tumor was visualized by 99mTc-DMSA (300-370 MBq) in 10 of 17 patients (58%). In 8 of 22 patients (36%), lymph node metastases were present at the time of diagnosis, as confirmed by histopathology and histochemistry after surgery (all <2 mm). Preoperatively, neither scan was able to detect lymph node involvement in these patients (0/8).
Conclusion: Both 99mTc-DMSA and 111In-octreotide studies have similar sensitivity to localize primary MTC; however, these scans are not able to detect small lymph node involvement (micrometastases) before initial surgery. Unfortunately, both scans have no clinical implication for preoperative staging in patients with MTC.