Retention index of thallium-201 single photon emission computerised tomography (SPECT) as an indicator of metastasis in adenocarcinoma of the lung

We examined the relationship between the retention of thallium-201 (201Tl) on a delayed scan and the metastatic potential of adenocarcinomas of the lung. We studied 43 patients with adenocarcinoma of the lung and divided them into two groups according to the presence or absence of lymph node metastasis. 201Tl single photon emission computerised tomography (SPECT) was conducted twice: 15 min (early scan) and 120 min (delayed scan) after intravenous injection of 3 mCi of 201Tl chloride. We calculated the retention index in order to evaluate the degree of 201Tl retention in the primary tumour. The retention indices were significantly higher in the group that was positive for lymph node metastasis than in the negative group. In adenocarcinomas with high metastatic potential, 201Tl SPECT demonstrated slow washout or increased retention on the delayed scan. The retention index of 201Tl SPECT is a useful indicator of metastatic potential, thereby facilitating the prediction of prognosis, and provides insight into the relationship between 201Tl uptake and malignancy. This is the first report demonstrating a significant relationship between the retention of 201Tl SPECT and lymph node metastasis.

[A case of occult breast carcinoma with micronodular shadows on chest x-ray film]

A 57-year-old woman was admitted to our hospital for the evaluation of roentgenological micronodular shadows of the bilateral middle and lower lung fields. Physical findings were normal except for left axillary lymph adenopathy. The level of tumor marker NCC-ST-439 was markedly elevated (2800 U/ml). Histological examination of the transbronchial biopsy and the swollen lymph node biopsy specimens showed proliferation of identical tumor cells. Breast or lung carcinoma was suspected as the primary site. Echogram of the left breast showed microcalcification without a mass. The biopsy specimen obtained from the calcified lesion indicated occult breast carcinoma. From these findings the diffuse micronodular shadows on the chest roentgenogram were considered to be the metastatic lesions of occult breast carcinoma. This case indicates that occult breast carcinoma should be considered as a possible primary site for diffuse pulmonary metastatic lesions.