Abstract: We demonstrate a new diagnostic method, the Photodynamic Infrared Spectroscoppy (PDIS), which is able to detect circulating tumor clusters and circulating tumor cells in the circulatory system. In particular the circulating tumor clusters are agreed as the main cause for metastases formation and therefore for the cancer mortality. The cancer mortality rate is unchanged worldwide in the last twenty years, indicating the absence of clinically effective metastases prevention therapies. No diagnostic method is existing, which allows to detect tumor clusters in vivo in the blood, which is the prerequisite for tumor cluster destruction and metastases prevention. The PDIS method is based on photodynamic physics and high resolution spectroscopy and is using calibrated spectroscopic data for the diagnostic analysis of the blood screening spectra. In the paper we are focussing to brest cancer diagnostics using the photosensitizer Indocyangreen. A flow appartus is described, which enables to calibrate the fluorescence spectra of single tumor cells and single tumor clusters. Due to the calibrated diagnostic data, the PDIS enables the identification of circulating tumot cells and tumor clusters in the bloodstream with the ultimate accuracy of one cluster per 6 l blood and with a sensitivity of 98%. Circulating tumor cell clusters are formed only in solid tumors, that’s why they are appropriate objects to validate cancer treatments and to recognice cancer formation. Due to the one-to one correspondence between tumor clusters in blood and the existence of solid tumors in the organism, the PDIS as diagnostic method can be used to control and to verify any oncologic treatment with respect to its clinical efficay. The common "wait and hope" strategy after finishing a chemotheraypy can be replaced by an effective follow-up strategy. Furthermore, the PDIS diagnostics can be used to recognize a tumor formation in the earliest possible stage, the carcinom in-situ stage. Finally the in-vivo detection of tumor clusters in the blood enables the immediate and controlled destruction of the these clusters by Photodynamic Therapy or other oncologic methods and therefore an increase of the overall survival of cancer patients and a decrease of the cancer mortalitay rate.Abstract: We demonstrate a new diagnostic method, the Photodynamic Infrared Spectroscoppy (PDIS), which is able to detect circulating tumor clusters and circulating tumor cells in the circulatory system. In particular the circulating tumor clusters are agreed as the main cause for metastases formation and therefore for the cancer mortality. The cancer mortal...Show More