A Quite Large, Hard Lump...about An Inch All Around. It

A quite large, hard lump...about an inch all around. It isn't sore but it's big. About an inch above right breast. I've had lymphatic cancer in 2011. I had a round of chemo...and it apparently was completely gone. So, yes I'm a bit scared as this lump just appeared. Within last hour. What could it be? It's not sore. Just quite big.