Protoporphyrin IX occurs naturally in colorectal cancers and their metastases

Colorectal cancers exhibit a red fluorescence. The nature of the responsibl e fluorophore and its eventual diagnostic potential were investigated. Thir ty-three consecutive colorectal resection specimen, 32 of which with histol ogically confirmed cancer, and a total of 1053 palpable mesenteric nodes we re fluorimetrically characterized pr vivo. Furthermore, frozen material fro m 28 patients was analyzed, selected for the availability of primary tumor material and metastatic tissue, e.g., lymphatic and liver metastases from t he same patient. Biochemical characterization was carried out through chemi cal extraction and reversed phase high-performance liquid chromatography. T he fluorescence spectra of tissues, tissue extracts, and standard solutions of porphyrins were determined using a pulsed solid-state laser system for excitation and an imaging polychromator, together with an intensified CCD c amera for time-delayed observation. Protoporphyrin IX (PpIX) was identified as the predominant fluorophore in primary tumors and their metastases, The fluorophore occurred in the absence of necrosis and in sterile locations. In untreated cases (n = 24), PpIX fluorescence discriminates metastatically involved lymph nodes from all other palpable nodes with a sensitivity of 6 2% at a specificity of 78% (P < 0.0001). After neoadjuvant treatment of rec tal cancer, the PpIX fluorescence level of the primary tumors was reduced a nd a discrimination of lymph nodes based on PpIX-fluorescence was impossibl e. We conclude that colorectal cancer metastases accumulate diagnostic leve ls of endogenous PpIX as a result of a tumor-specific metabolic alteration.