I remember the days when it wasn't considered baroque and extravagant to add -lily to the end of words that were meant to describe (or 'modify') verbs: 'we had a leisurely drive' but 'we drove leisurelily'. But if you look for it in the dictionary, it won't be there: why not? Why is OK to say 'livelily' but not 'leisurelily' on the same principle? Yes, it's a bit awkward, but adding 'lily' for the sake of a grammatical distinction always was. But the thing is, I still feel, when I read that benign tumour cells 'tend to grow more slowly and orderly' that something is missing. The 'slowly' part is all right, since it has an adverbial capacity built in, if you like. But 'orderly' is an adjective without that adverbial reach. I feel that it ought to be 'slowly and orderlily'. Perhaps that sounds too floral and fussy for our era.