Detection of colorectal carcinomas by intraoperative RIS in addition to preoperative RIS: surgical and immunohistochemical findings

Abstract

The immunoscintigraphic detection of tumour foci < 1 cm in diameter fails even with single photon emission tomography (SPET) owing to low contrast against background activity. In an attempt to improve detection of macroscopically invisible tumour spread, intraoperative scintimetry (IOSM) with a hand-held gamma-probe was performed in addition to SPET 24–30 and 41–48 h after injection of the technetium-99m carcinoembryonic antigen (CEA MoA) on 12 patients with colorectal carcinoma and 3 patients with different neoplastic and inflammatory diseases. Tumour specimens were measured in vitro in a gamma well counter. For comparison, the presence and amount of CEA in the tumour cells were evaluated immunohistochemically. After modification, the gamma-probe originally designed for iodine-131 was 20 times more sensitive; activities of ⁹⁹Tc located close to the collimator hole were measured with absolute sensitivity of 100 cps = 2.5 kBq ^99mTc. The unfavourably high background activity affected both the in vitro and in vivo analysis: SPET results had been considered positive in 8 of 15 cases. In vitro tumour/non-tumour (t/nt) ratios > 2.0 were found in 4 cases. In vivo IOSM resulted in t/nt ratios >2.0 in only 3 patients. In most cases, there was no coincidence of elevated t/nt ratios from the different methods. A correlation was derived between positive immunoscintimetric in vitro findings and immunohistochemically proven interstitial localization of CEA in tumor cells. In conclusion, the measurement technique of IOSM seems adequate, but clinical success will depend on a more specific enrichment of MoA in tumour tissue. Future in vivo studies should be performed mainly in cases with a positive immunohistochemistry (interstitial CEA localization) result for the primary tumour.