Many women are unaware of the fact that breast cancer does not always show up as an obvious lump. The lump might be so small that it is undetectable. There are lots of other signs of breast cancer and it's definitely worth knowing them so that you know when to go and get checked out. The sooner breast cancer is diagnosed, the better and early detection can save your life.
A swollen breast is one sign of breast cancer, and if there is any dimpling or lumpiness in that breast that can be another sign. You might also have a lump or swelling in the armpits and underarm pain. Your nipple might change in appearance, such as inverting or beginning to leak.
There are some really good guides for this online with pictures of what it might look like. If you have any reason to think you might have or get breast cancer (this includes men and women) then I would go and look up the signs.