weight really stable

I think our bodies secretly store those calories somewhere, and dump them into our systems as a weight gain when we least expect it. 

My onco does pay attention to my weight, but I think it's because there are so many things going on that could cause me to gain or lose weight right now.  Probably the least of them is a cancer recurrence.  I don't mean that's the least important -- I mean it's the least likely to cause a weight change.  "Cancer cachexia" doesn't happen early with cancer, especially in fairly early-stage BC.  A two- or three-cm tumor (or less) really doesn't suck up that many more calories than, say, a biceps muscle we've exercised.

OTOH, I had lost 4 pounds last summer, and kept it off through the fall.  That's not a huge amount -- maybe around 2-1/2 to 3% of my body weight.  When I went for my most recent onco recheck, she noted that I had lost some weight since my previous visit and she asked, "Was that intentional?".  I said it was, and she said, "Good for you!".  I'm on Arimidex, so it's a challenge to maintain a stable weight and even harder to lose weight.

Unfortunately, I had an unwanted Christmas present this year (as my PCP put it this morning) -- I've gained back the 4 pounds.

I'd say stop worrying if you are feeling good and your appetite is strong and your energy level is "normal" (I know, those can be problems after BC treatment). But, ask your onco.  I'll bet he/she will brag on you for having a stable weight.

otter