Scintigraphic TNM Staging of Tumors: A Proposition

TO THE EDITOR: Very often, local nodal metastases and distant metastases in lungs and bones from differentiated thyroid cancer are detected only by ¹³¹I whole-body scintigraphy, or more accurately by ¹³¹I SPECT/CT, during the first radioablation after total thyroidectomy. In a recently published article, Schmidt et al. (1) showed ¹³¹I SPECT/CT to have a definite advantage in the demonstration of nodal metastases in the neck from differentiated thyroid cancer. Another recent article, by Spanu et al. (2), reported that ¹³¹I SPECT/CT had incremental utility for the detection of local nodal and distant metastases in lungs and bones from differentiated thyroid cancer. Chest radiography and even CT can miss early pulmonary and skeletal metastases. Contrast-enhanced CT is not recommended before radioiodine ablation.

The usefulness of TNM staging as a major prognostic indicator in the management of differentiated thyroid cancer has been reemphasized in recent years (3). Postoperative histopathologic examination of thyroidectomy specimens facilitates pathologic TNM (pTNM) staging but does not take into account other prognostic variables such as distant metastases when they are not detected clinically or by radiologic studies, before thyroidectomy. In this context, the utility of radioiodine scintigraphy is significant.

The following case report illustrates my point well. A 36-y-old man presenting with a 2-cm solitary nodule in the right lobe of the thyroid and enlarged ipsilateral cervical nodes underwent total thyroidectomy and right modified radical neck dissection. His chest radiograph showed no evidence of pulmonary metastases. Histopathologic examination found papillary carcinoma with metastatic cervical nodes, and hence the stage was defined as pT1N1bMx. Preablation whole-body scintigraphy revealed residual thyroid tissue, nodal metastases, and focal as well as diffuse radioiodine accumulation in the lungs bilaterally. Lung uptake was confirmed on SPECT/CT, thus altering the stage of the disease from Mx to M1. Scintigraphy-assisted staging (“sTNM” staging, with the stage in this patient defined as “sT1N1bM1”) is more accurate than pTNM staging in this setting. Similarly, with the advent of PET/CT, which is currently done for several oncologic indications, the scintigraphic staging of a tumor can be more precise than the conventional TNM staging.