Cribriform pattern in prostate cancer is a key consideration in classifying and understanding the aggressiveness of the disease and is often associated with higher risk of recurrence and poorer prognosis.

I do not think it implies anything - cribriform literary needs to be measured to determine if they are "big". Measuring cribriform for actual size is a novel idea and many pathology labs probably are not doing it. Until relatively recently cribriform were not even included as observation in pathology report and IDC was often bunched and mixed together with true ductal carcinoma which is completely different entity. All in all, "big" cribriform just has more mutations than small ones, and small ones have more than a plain gleason 4 cell. The more mutation there is- the more aggressive cancer is, and sometimes those cells are less susceptible to radiation because they have so many mutations and possibly even better reparation mechanisms of their DNA. There were many studies but nobody knows with absolute certainty why cribriform are "bad news" but they are, so treatment has to be adjusted accordingly, meaning that treatment has to be more aggressive when they are present.
If you really wish to know the size of cribriform you should send your slides to a lab that measures them and getting second opinion on pathology is a good idea anyways. If it is truly the most aggressive big cribriform, it is the most resilient bugger. For that reason recurrence is possibility with either RP or RT but as with anything else in life it does not happen always ! You should just have one thing in mind thou - if you have radiation as initial treatment you can not irradiate that same area twice. If you have RP as initial treatment you have radiation option as an "ace" up your sleeve.