We discuss limitations of the known methods of IR imaging in diagnostics of breast cancer. In conclusion we show that the known methods, based on simple observation of external temperature distribution, are not fully effective. Even advanced pattern recognition could not help in analysis of static images. May active dynamic thermography, known in non-destructive testing of materials, be of any help in breast cancer diagnostics? Analysis of thermal transients forced by external thermal excitation shows, even on simple models, that one may expect a visible improvement in resolution after such excitation. Applied models allow analysis of both static and active thermograms. Basing on the models one may recognise elements of the internal structure of a breast not visible in static pictures. This method, new in clinical practice, seems to be promising, but requires further studies.