Any increase in tissue size is not necessarily neoplasia. Here is an example of left ventricular cardiac hypertrophy in which there has been an increase in the size of the myocardial fibers in response to an increased pressure load from hypertension. With hypertrophy, the cells increase in size, but the cells do not increase in number. Except for being larger, the cells are normal in appearance.
Alterations in cell growth can be physiologic (normal responses to stimuli) or pathologic. These alterations of cell growth are potentially reversible and include:
Hypertrophy: an increase in cell size. Increase in skeletal muscle fiber size is a physiologic response to exercise, but the cardiac hypertrophy shown above is a pathologic response to abnormally elevated blood pressure.
Hyperplasia: an increase in the number of cells. Postpartum breast lobules undergo hyperplasia for lactation, but endometrial hyperplasia in a postmenopausal woman is abnormal.