99mTc MIBI scintimammography is a promising diagnostic technique for cancer detection. Using a dedicated Small Field Of View Gamma Camera (SFOVGC) with the high spatial resolution recently developed, it is possible to improve the sensitivity and to achieve images in projections similar to mammography with the breast under moderate compression. This new technique is called Single Photon Emission Mammography (SPEM). Several factors affect the imaging of small cancers; breast thickness, tumor-collimator distance and body activity. A phantom study was performed to assess the role of breast compression in scintimammography. In this work we analyze the intensity and the energy distribution of Compton scattering affecting the breast scintigraphy, by a Germanium detector and by SFOVCG. Five patients with 7 to 18 mm sized cancer were studied. The intensity of Compton scattering resulted from 4 to 10 times greater than true events. The fundamental role played by breast compression to improve the scintimammographic sensitivity is discussed.