Studies of human families seem to show that heredity has a slight influence, but in the frequency of tumors such statistical evidence is of little value.

The question of inheritance has much bearing on the origin of tumors.

If the tumor is accidental and due entirely to extraneous causes, inheritance is not probable; but if there is some predisposition to tumor formation in certain individuals due to some peculiarity, then inheritance may exert an influence.
The question as to whether tumors are an increasing cause of disease is equally difficult of solution.

The mortality statistics, if taken at their face value, show an enormous increase in frequency; but there are many factors which must be considered and which render the decision difficult and doubtful.

Tumors are largely a prerogative of age, and the increased duration of life which preventive medicine has brought about brings more people into the age when tumors are more common.