Sentence:  Here there may be an analogy with cancer : we can detect cancers by their rapidly accelerating growth , determinable only when related to the more normal rate of healthy <WSD>growth</WSD> . 
Meaning of the word marked with <WSD> tags:  (biology) the process of an individual organism growing organically; a purely biological unfolding of events involved in an organism changing gradually from a simple to a more complex level