Sorry your fish is sick. I checked The Manual of Fish Health (A great resource).
Do the lumps resemble molten candle wax? If so, it is probably fish pox. Lymphocytosis is usually one lump not 2-3 like yours has. There's no effective treatment other than a water change and up the temp by approx 9-18 F above normal.
The good news is, it's not painful nor fatal. It is not very contagious. Its most common in coldwater tanks & ponds.
So my advice is watch him. If behavior, appetite, etc remain healthy, don't worry. It may disappear & recur. Regardless, it's mainly unsightly, not dangerous.
Obviously, additional problems rule out this diagnosis.