An application of FTIR spectroscopic imaging for the identification and visualization of early micrometastasisfrom breast cancer to lungs in a murine model is shown. Spectroscopic and histological examination is focusedon lung cross-sections derived from animals at the early phase of metastasis (early micrometastasis, EM) ascompared to healthy control (HC) and late phase of metastasis (advanced macrometastasis, AM) using murinemodel of metastatic breast cancer with 4T1 cells orthotopically inoculated. FTIR imaging allows for a detailed,objective and label-free differentiation and visualization of EM foci including large and small micrometastases aswell as single cancer cells grouped in clusters. An effect of the EM phase on the entire lung tissue matrix as wellas characteristic biochemical profiles for HC and advanced macrometastasis were determined from morpholo-gical and spectroscopic points of view. The extraordinary sensitivity of FTIR imaging toward EM detection anddiscrimination of AM borders confirms its applicability as a complementary tool for the histopathological as-sessment of the metastatic cancer progression.