It looks like the beginning stages of a twig gall. Galls are often caused by chemicals that affect growth and cause abnormalities, chemicals released by either diseases or insects feeding. The insects that most commonly cause galls are wasps, mites, aphids, and flies, not necessarily in that order.

I'd remove it with a sharp pair of sterilized pruning shears, or use a fresh straight-edged razor blade or utility knife blade. Cut back a good distance proximal to the abnormality.

Al

Hi,

I found a similar thread somewhere on the net with the same advise so I gave it a try, cut the plant back some 5 cm, and one month later there seems to be some development at the top three leaves' nodes.

Looks promising?

And yes, I completely failed at performing a clean cut... poor plant. :-)

Some more specific guidance can be had if you're interested. A picture of the full plant would be nice, though.

Al

Well, that was fast - look who's waving! :-)

Most certainly interested, thanks. :-)

A few leaves have an abnormal shape - according to information I've found on the net that could be a side-effect of whatever caused the removed lump.

Three roots grew out of the pot's drainage holes and they look healthy (not squishy or discolored).

Two weeks have passed and I'd say cutting the plant back was a success. :)

Thanks tapla for your advise!