As in dogs, tumor size is an important prognostic factor, although for tumors less than three centimeters the individual size is less predictive. According to one study, cats with tumors less than three cm had an average survival time of 21 months, and cats with tumors greater than three cm had an average survival of 12 months. About 10 percent of cat mammary tumors have estrogen receptors, so spaying at the time of surgery has little effect on recurrence or survival time.
Tumor size is a key prognostic factor for both dogs and cats, with individual size becoming less significant for smaller tumors.  The presence of estrogen receptors in some cat mammary tumors has little impact on the outcome of surgery.