It's reported that Noonan syndrome can come in association with multiple myoblastomas (also known as Abrikossoff tumors or granular-cell tumors). These tumors are characterized by low malignant potential and it might be that they're of neuronal origin (from Schwann cells). It's of note that they're histomorphologically different from neurofibromas, so that patients affected by Noonan syndrome showing multiple granular cell tumors cannot be considered as affected by the well known Neurofibromatosis-Noonan syndrome.
This association is very very rare indeed, since just three or four cases have been described.
These tumors must be surgically removed either by complete ablation or by excisional biopsy (i.e. removing just a part of the tumor).
Find out more on the references cited below.
References
Lohmann DR, Gillessen-Kaesbach G. Multiple subcutaneous granular-cell tumours in a patient with Noonan syndrome. Clin Dysmorphol. 2000 Oct;9(4):301-2.
Fryssira H, Leventopoulos G, Psoni S, Kitsiou-Tzeli S, Stavrianeas N, Kanavakis E. Tumor development in three patients with Noonan syndrome. Eur J Pediatr. 2008 Sep;167(9):1025-31. Epub 2007 Dec 5.
Rose B, Tamvakopoulos GS, Yeung E, Pollock R, Skinner J, Briggs T, Cannon S. Granular cell tumours: a rare entity in the musculoskeletal system. Sarcoma. 2009;2009:765927.
Fryssira H, Leventopoulos G, Psoni S, Kitsiou-Tzeli S, Stavrianeas N, Kanavakis E. Tumor development in three patients with Noonan syndrome. Eur J Pediatr. 2008 Sep;167(9):1025-31. Epub 2007 Dec 5.
Rose B, Tamvakopoulos GS, Yeung E, Pollock R, Skinner J, Briggs T, Cannon S. Granular cell tumours: a rare entity in the musculoskeletal system. Sarcoma. 2009;2009:765927.
