c-KIT exon 11 mutation test in mast cell tumours
Mast cell tumours are among the skin tumours of dogs, and their behaviour varies from harmless to aggressive. The c-KIT test looks for one particular change in the tumour’s DNA — a duplication in exon 11 of the c-KIT gene. It helps the vet and the oncologist judge how the tumour may behave and which approach to consider; it is not a test for whether a lump is a tumour.
What it shows
The c-KIT gene carries the instructions for KIT, a receptor on the surface of mast cells that tells them to grow and divide. In some mast cell tumours this gene is changed so that the receptor stays switched on all the time. The common change is an internal tandem duplication (ITD): a short piece of the gene is copied twice in a row. A PCR test copies this region of the tumour’s DNA and checks whether the piece is longer than expected.
The line on the form refers to exon 11, one section of the gene. Some laboratories test exon 8 as well and report it on a separate line; in canine skin mast cell tumours exon 11 duplications are found in about 20–30% of tumours, exon 8 duplications in 2–5%. In dogs both tests can be part of a mast cell tumour prognostic panel, together with grade and markers of cell division, or ordered on their own.
Higher than reference — what it may be a sign of
- Mutation detected (positive) — the tumour carries an exon 11 duplication. In dogs this finding is linked with a higher rate of spread and of death from the tumour, so it is one of the markers that point to more aggressive behaviour. A small pilot study found it in 2 of 6 high-grade tumours and in none of 4 low-grade ones.
- Why the oncologist wants it — medicines that block the KIT receptor exist, and the result helps the oncologist choose an approach; the choice itself is the oncologist’s decision.
Lower than reference
No mutation detected (negative) — the tumour has no exon 11 duplication in the region tested. That is the usual finding, since most mast cell tumours do not carry it. It does not mean the tumour is harmless: grade, size, location and spread are judged separately. The result is one of several facts the oncologist weighs.
Look at together with
- Histological grade of the tumour — the main description of how the tumour looks; two grading systems are in use, so the report names the system.
- Markers of cell division such as Ki-67 and KIT staining pattern (immunohistochemistry) — often part of the same prognostic panel.
- Exon 8 line, if tested — expected to have a similar link to targeted medicines, but no link to prognosis has been established.
- PARR — another DNA test from a tumour sample, but for lymphocytes, not mast cells.
Units and conversion
The result has no units. It is reported in words: mutation detected / positive or no mutation detected / negative, sometimes with “internal tandem duplication” spelled out. In the app the result is stored as text.
Reference range
The expected result is on your lab’s form; for this test the reference is “no mutation detected”. A positive result is not a diagnosis on its own — the vet reads it together with the histology report, grade and staging.
Cats and dogs
Most skin mast cell tumours in cats are benign, though some come back after removal. More aggressive forms occur, in the intestine or internal organs, usually the spleen and/or liver. For cats one laboratory offers an exon 8 test rather than exon 11; mutations are found more often in the aggressive tumours outside the skin.
The exon 11 test is mainly a dog test. Mast cell tumours in dogs range widely in behaviour, and the mutation is one of several markers used to describe that behaviour. The same exon 11 change also occurs in some gastrointestinal stromal tumours of dogs.
Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.
Sources
- Michigan State University Veterinary Diagnostic Laboratory. Detecting c-Kit Mutations.
- Villalobos AE. Lymphocytic, Histiocytic, and Related Cutaneous Tumors in Animals (mast cell tumors). Merck Veterinary Manual, professional version.
- Targeted Antineoplastic Agents in Animals. Merck Veterinary Manual, professional version.
- Neto RT, Cagnini DQ, Amorim RL. Mutations in C-KIT exon 11 in canine cutaneous mast cell tumors. BMC Proceedings 2013;7(Suppl 2):P56.
This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.