Biologic variations of tumors

Few tumors are so heterogeneous in their growth rates and patterns of metastasis as breast cancer. In general, the clinical phase of this disease is much longer than that of most other tumors. It is assumed that the preclinical phase is similarly long and this is one reason that the use of screening mammography has reduced breast cancer mortality. Mammography is not equally effective in all patient populations, but it has not yet been possible to precisely define those populations of women more or less likely to benefit from periodic mammography. Future studies should place greater emphasis on the correlation between frequency of mammography and biologic variations.