Hamartoma

A hamartoma is a:

1. Disorganized (non-neoplastic) growth (that may mimic a true neoplasm).
   • May be clonal.
   • May have recurrent genetic translocations.
2. Composed of tissue of the region within it is found.

Micrograph of a pulmonary hamartoma. H&E stain.

Note 1

1. If #2 does not apply it is a choristoma.
2. "Disorganized" in #1 separates it from:
   • Hypertrophy and hyperplasia - which may be physiologic processes.
3. The key differences between cancer and hamartoma are the ability of cancer to:
   • Invade/destroy surrounding tissue.
   • Metastasize.
4. Considered clinically, growth is the difference between a benign tumour (measurable growth rate) and a hamartoma (no growth vis-à-vis the surrounding tissue).
5. Hamartomas often consist of:
   • Multiple cell types, e.g. Peutz-Jeghers polyps consist of normal submucosal elements.
   • Have a well-circumscribed border.

Note 2

There is much confusion in this area as:

• Clonality is usually considered a characteristic of neoplasms.
• The line between benign tumour and hamartoma is thin, if one considers that a hamartoma can be clonal and some benign tumours have a slow growth rate.
• If one considers choristoma (hamartoma's cousin), the line between benign tumour (e.g. teratoma/dermoid cyst) and choristoma is thin.

A more useful definition of hamartoma might be:

1. Architecturally disorganized tissue that appears to be native to the site.
2. No significant growth (vis-à-vis the surrounding tissue).

Site specific

• Mammary hamartoma.
• Pulmonary hamartoma.
• Splenic hamartoma.
• Neurocristic hamartoma.
• Peutz-Jeghers polyp.
• Fibrous hamartoma of infancy.

See also

• Basics.
• Cancer.
• Odontoma.