The use of Tc-99m-phytate for sentinel node mapping in melanoma, breast cancer and vulvar cancer: a study of 100 cases

Sentinel node mapping reduces surgical morbidity and allows the use of more accurate tumour staging techniques. Radionuclide studies are preferentiall y performed using small colloids, which have limited availability in our co untry. The possibility of using phytate for sentinel node mapping was raise d because of the similarity between its biodistribution and that of nanocol loids in the reticulo-endothelial system. In this paper we evaluated the us e of Tc-99m-phytate for sentinel node mapping, correlating the histopatholo gical results with the status of the rest of the lymph node chain in differ ent malignant tumours. A total of 100 patients were studied. group 1 consis ted of 62 patients with breast cancer, group 2 of 20 patients with melanoma and group 3 of 18 patients with vulvar carcinoma. Lymph node scintigraphy was carried out after injecting Tc-99m-phytate subdermally, and the sentine l node projection was marked on the skin. After 18-24 h, intraoperative sen tinel node localisation was performed using a gamma probe (combined with vi sual localisation using patent blue dye) in 75 patients, and lymph node dis section was then carried out. Radionuclide scintigraphy identified the sent inel node in 98% of all studies. Intraoperative detection using the gamma p robe was equally efficient: group 1=93% (38/41). group 2=95% (18/19) and gr oup 3=100% (15/15). The sentinel node was involved in 41% 31% and 20% of ca ses in groups 1, 2 and 3, respeciively. Among the patients with positive no des, the sentinel node was the only one affected in 53% of group 1, 50% of group 2 and 67% of group 3 cases. The method's negative predictive value wa s 91% in group 1 and 100% in the other groups. One false-negative study occ urred in a patient who had a multifocal tumour and an intraparenchymatous l ymph node; another occurred in a patient with a macroscopically affected no de found during surgery. There were no side-effects related to the Tc-99m-p hytate. It is concluded that scintigraphic and intraoperative sentinel node identification was satisfactorily performed using 99mTc-phytate. The resul ts were comparable to those previously described in the literature using ot her radiopharmaceuticals. Easy availability and low cost justify the use of phytate in our practice.