My son has nf1 and came and showed me a lump under his skin on the lower part of his chest. size of marble it hurts sharp pain, looks bruised?

Pediatric neuro: May represent a neurofibroma. Worthwhile getting your son to a pediatric neurologist or neurosurgeon to assess for other lesions.

Neurofibromatoma: This looks very much like what we call a plexiform neurofibroma, they can be quite painful and do grow over time. I would recommend you see a pediatric neurosurgeon for evaluation and possible excision both for pain management and not let it get too large.

He should: He should have this biopsied. It is probably one of the painful tumors made out of muscle, nerves, blood vessels or fat. See dermatologist to find out.