Following the traces of lung cancer

Surgeon Naia Uribe-Etxebarria has used a radioactive substance which, injected into a lung tumour, enables the detection of the path that the carcinoma intends to take in order to propagate itself. Concretely she applied technetium 99 in resectable non-small cell lung cancers (NSCLC) at an early stage (I or II), and in an intraoperative manner. Thanks to this, she detected with precision the sentinel node (SNOL); the primary node or ganglion of cells to receive lymphatic drainage from the tumour and, thus, most probably the one that will be affected by the tumour and give rise to its propagation. Her PhD thesis, defended at the University of the Basque Country (UPV/EHU), is entitled "Utility of the intraoperative study of the sentinel node with technetium 99 for the staging of non-small cell lung carcinoma."

80 % of lung cancers are of the NSCLC type, of which 25-30 % are at an early stage (I or II). In these cases, surgical resection is the most effective treatment. Concretely, patients are usually subjected to anatomical resection of the pulmonary lobe or of the whole lung, together with a ganglionary dissection. This dissection helps to define the extension and seriousness (stage) of the cancer and decide on the postoperative treatment to be carried out, given that the lymphatic ganglia being affected or not is highly indicative of the progress of the cancer.

48 patients at the Cruces hospital

With regard to this, a biopsy of the sentinel node is a standard technique for determining the ganglionary stage of breast cancer or melanoma, but neither this nor tinctures are effective against lung cancer. Previous research showed that the radiotracer technique is the most effective in this case, and Ms Uribe-Etxebarria opted concretely for technetium 99 colloidal sulphate.

The research was carried out on 48 patients at the Cruces Hospital in Barakaldo (in the Basque province of Bizkaia and near Bilbao), who were injected with a dose of 0.25 millicuries within the tumour, divided into its four quadrants. After ten minutes, the radiation of the tumour and the intrathoracic ganglionary stages were measured with a manual gamma radiation counter. Migration of the radioisotope was deemed satisfactory when the radiation was thrice that marked in the primary tumour. Then, the usual operation was carried out, including tumour extraction, ganglionary sampling and recommended grade of extirpation of ganglia, depending on the case. Subsequently, gamma measurement was undertaken on these samples outside the organism. Sentinel nodes are considered to be those which, once again, showed radiation was thrice that of the base value, as this radioactivity shows the path traced by the substance and, it is thus deduced, by the disease.

Positive results of over 90%

The results show that identification of the lung sentinel node is possible with the use of radioisotopes in an intraoperative manner. Sentinel nodes were identified in 100 % of cases, while the sensitivity, precision and negative predictive value of the technique gave values close to or greater than 90 %. There was a rate of negative false values of 11.76 %; i.e. there were cases in which radioactivity was not detected in a zone in which there was, in fact, a sentinel node. It should also be pointed out that sentinel nodes and lymphatic nodes with greatest risk of metastasis are those located near the tumour. Moreover, there may be cases in which there is more than one sentinel node (in two of the 48 cases, two were found).

Ms Uribe-Etxebarria concludes that the technique studied enhances the ganglionary staging of the patients with resectable non-small cell lung cancers (NSCLC). Detecting the sentinel node provides clues to the affected zone. This enables the pathologist to focus on a smaller number of ganglia, and carry out the pertinent techniques on these for the precise diagnosis of micrometastasis and isolated tumour cells. Moreover, residual radioactivity after resection can detect small ganglia which otherwise may go unnoticed.

Nevertheless, the researcher also specifies that this technique has certain limitations. For example, as regards identifying lymphatic ganglia close to the tumour, as the recording of the probe in this zone is very affected by the recording of the tumour itself (the shine through effect). It would be impossible to measure separately the radioactivity of the intralobular ganglia adjoining the tumour. That is why the two false negatives mentioned above appeared.