Do doctors often misdiagnose cancer as something else?

Yes: If a lesion is seen and an attempt at biopsy made, the needle being used may penetrate and go thru the lesion to report it as benign. If a mass is palpated in muscle and at random biopsy taken, the lesion may be heterogeneous and a benign site sampled when there is a malignancy. Best to perform a total excisional biopsy to guarantee proper sampling. X rays can also be misinterpreted initially.

Possible: Initial symptoms may not be indicative of cancer hence doctors may not aggressively pursue further testing leading to delayed diagnosis or symptoms may suggest a less serious illness