stock69 is right....but there are variations as far as symptoms, frequency of occurrence, etc... I ran my first 3-4 cycles which included compounds like deca, tren and test and never had any gyno symptoms...then BHAM, suddenly it hit...I didn't get the tenderness or small "lumps"...but you could feel a large fibrous mass underneath the muslce....I tried the letro / dostinex route.... helped the first time around to the point where it was practically non-existent after I got off the cycle.... then next time around, it came back again... so the letro/dostinex will help for some, but not all...but always worth a shot....
IMO, it's always to be safe than sorry, always good to run a low dosage AI with any aromatizing compound (i.e. test)...and run some dostinex with progestins such as tren or deca