oxymoron....I stand to be corrected but I think that bednobs is referring to survival rates which have nothing to do with the definition of "remission" which is not time related.
If after treatment or indeed less commonly without treatment, you cancer hasn´t grown any larger and you are symptom free.....then you are said to be in remission. The cancerous lump mat still be present clinically or evident on X-Ray, providing it isnt getting any bigger, then you are in remission.
From your story, I gather that you have had a lump removed from your breast followed by Radiotherapy and if the lump has not returned, chest X-Ray and body scan is normal........then you are in "remission"