Silent endocrine tumors. A steady-state analysis of the effects of changes in cell number for biological feedback systems.

Some tumors of hormonal organs are clinically active, while others are not. The "silent" tumors may be discovered by accident or because of effects due to their increase in size. From a simple steady state analysis of hormonal feedback systems follows that hormonal cell multiplication does not significantly influence the systems steady state behaviour (hence the clinical silence).--Exceptions to this rule occur in three situations: when the gain of the system is low; when the growth concerns cells with isolated sensor or reference functions; or because of the growth of autonomous cells. In many biological systems the dangerous situation of clamping to low levels upon sensor cell multiplication has been prevented by lumping, such as the combination of sensor and comparator functions into sensor-comparator cells.