It can spread without breaking out of the capsule; they are two different things.
Imagine your prostate is an orange in a fruit bowl. The inside of the orange goes bad but the outer skin still looks absolutely fine - that would be a T1 or a T2 depending how bad it is inside. If the orange gets really bad, there may be black marks on the skin or it may even break down so you can see some of the inside badness - that is a T3. If the orange goes bad and the skin goes mouldy, the mould spreads to the apple next to it in the fruit bowl - that is a T4.
Now imagine that the orange was on top of the fruit bowl, with other fruit below it. It looks fine on the outside but the rotten flesh turns to liquid and seeps into the bottom of the bowl and from there to some grapes which now also go mouldy - that is N1
If you stick a syringe into the bad orange and draw off the juice to put into a cake, the cake is going to taste pretty bad and will quickly turn mouldy. The outer skin of the orange might still be intact but the inside has ruined a nice cake - that is M1.