  Chemotherapy is a class of cancer treatment that uses drugs to kill cancer
cells. A typical chemotherapeutic protocol consists of several drugs delivered
in cycles of three weeks. We present mathematical analyses demonstrating the
existence of a maximum time between cycles of chemotherapy for a protocol to be
effective. A mathematical equation is derived, which relates such a maximum
time with the variables that govern the kinetics of the tumor and those
characterizing the chemotherapeutic treatment. Our results suggest that there
are compelling arguments supporting the use of dose-dense protocols. Finally,
we discuss the limitations of these protocols and suggest an alternative.
