The present invention deals with discrimination of malignant tissue from normal and benign tissue in a single patient on the basis of optical spectroscopic measurements. Starting from spectroscopic measurements in normal tissue, reference values are obtained for the normal class. With spectroscopic measurements in other tissues data points can be assigned to new class(es) when the spectral characteristics fall outside a threshold defining the reference class. Thresholds between different classes can also be defined. Finding (the transition to) malignant tissue is based on comparing the spectroscopic values to the classification threshold discriminating normal and benign versus malignant tissue. Thus, the basis of normal spectroscopic measurements is tuned to the individual patient characteristic. Discriminating the normal plus benign and malignant from that reference is more efficient compared to the reference of the all patient database.