Medical Oncologist
CION Cancer Clinics
Making sense of the c. and p. notation on your report | CION Cancer Clinics
The c. and p. lines on a genetic report are a precise address for the exact change a laboratory found, not a verdict on how serious it is. This page explains what each notation describes, why the same change is written twice, and why a short-looking change can matter more than a long one. At CION Cancer Clinics in Hyderabad, our oncologists review your family history with you and guide you to the right genetic counselling and testing.
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Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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Decoding the report
What do the letters after the gene name actually mean?
They are a precise address for the exact spelling change the laboratory found. One line, usually starting with "c.", describes the change in the gene's own instructions. A second line, usually starting with "p.", describes what that change does to the protein the gene builds. Together they tell a specialist exactly what was found, without any guesswork.
Why the same change is written twice
The gene is a set of instructions written in a code of four letters. The protein is what the cell actually builds by reading that code, using a different alphabet of building blocks. The "c." line describes the change where it happened, in the instructions. The "p." line translates that into what it does to the finished protein. Some reports show both, some show only one. Think of it as an address followed by a translation: the first tells a specialist exactly where to look on the map, and the second tells them what actually changed once they get there.
Why it looks alarming and usually is not
A string like this is designed for machines and specialists to be exact, not for a family to read at a glance. Its length has no bearing on how serious the finding is. A short, simple-looking change can matter far more than a long one.
The notation tells you exactly what changed. It does not, by itself, tell you what that change means for you.Two notations, one change
What is the difference between c. and p. notation?
Reports often print both lines one after the other. Each is answering a slightly different question.
c. notation
Describes the change at the level of the gene's own coding instructions, counting position from the start of that stretch of code. The letter after the position is usually a single-letter code for the building block involved.
p. notation
Describes what the change does to the finished protein, using three-letter short forms for the building blocks it swaps. It tells you the practical consequence, not just where the spelling changed.
Why the two numbers are not the same
The counting systems are different, so the position quoted in the "c." line and the position quoted in the "p." line will not match. Both can be correct at once.
When only one line appears
Some changes fall outside the stretch of code that becomes protein, so there is nothing for a "p." line to describe. A "c." line alone is not a lesser or incomplete result.
Not sure whether this applies to you?
Ask an oncologistWorking through it
How do you actually read one of these lines?
Start with the gene name
Usually written in capital italics just before the notation. This tells you which set of instructions is being discussed at all.
Check the transcript number beside it
A reference code the laboratory used as its map of that gene. The same change can be numbered differently against a different map, so this detail matters more than it looks.
Read the c. line as "where, and to what"
It names a position in the code and what the letter was changed to, added or removed. You do not need to translate it yourself.
Read the p. line as "what it does to the protein"
This is usually the part your doctor or counsellor will explain in plain terms, describing the practical effect rather than the raw spelling change.
Terms on the notation line
The words that go with the notation
- Coding sequence
- The stretch of a gene's instructions that actually gets turned into protein. The "c." in the notation refers to this.
- Transcript
- A specific, numbered reference version of a gene, used as the map against which a position is counted. It is why the transcript number is printed beside the notation.
- Exon
- One of several working sections of a gene's instructions, spliced together before being read. A report may mention which exon a change falls in.
- Missense change
- A single swap that changes one building block of the protein for another. It may or may not affect how the protein works.
- Nonsense change
- A change that creates an early stop signal, so the protein is cut short. These are more often, though not always, disruptive.
- Frameshift
- A change that adds or removes letters in a way that shifts how everything after it is read, usually scrambling the rest of the protein.
- Reference sequence
- The standard version of a gene against which your notation is compared. It is where the transcript number comes from, and why quoting it correctly matters when a report is compared against another.
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Did you know
Because the same change can be numbered against different reference transcripts, two reports on the same person, from two laboratories, can show two different-looking notations for the identical fault. It is one reason a counsellor asks for the transcript number, not just the notation, before comparing reports.
Being straight with you
What this page cannot tell you
It cannot tell you what your specific notation means for your health or your family's risk. Reading the code correctly is not the same as interpreting it, and the two are easy to confuse once you can sound the letters out.
It cannot replace the classification on the report
The notation only describes what changed, not whether that change is harmful. That judgement is a separate line on the report, decided by a laboratory scientist weighing evidence, and it is the line that actually matters for decisions. Two notations that look almost identical can carry completely different classifications, which is exactly why reading the code is not the same skill as interpreting it.
Who this does not apply to
If you have not had genetic testing, there is no notation on any report of yours to read. This page is for people already holding a result and trying to make sense of the string of letters on the page.
If a notation on your report does not match anything here, bring the whole page to your counsellor rather than trying to decode it alone.Questions we are asked
Common questions about variant notation
Why does my report only show a c. line and no p. line?
Some changes sit outside the part of the gene that becomes protein, so there is nothing for a p. line to describe. It is not a sign the result is incomplete or that something went wrong with the test.
My p. line ends in a question mark. What does that mean?
It usually means the exact effect on the protein could not be predicted with confidence from the DNA change alone. It is a laboratory convention, not a sign the test failed, and your counsellor can explain what it means in your case.
Can I tell how serious a variant is just from its notation?
No. The notation only describes the change itself. Whether it is harmful is a separate classification on the report, arrived at by weighing evidence the notation does not show.
Why do two labs write my same result differently?
Usually because they used different reference transcripts to count position. Check whether the transcript number matches before assuming the labs disagree about the finding itself.
Is a longer notation more serious than a short one?
No. Length reflects how the change happens to be written, not its impact. A short swap can matter more than a longer one, and the classification line is what tells you which.
Should I search my exact notation online?
You can, but a search result without your full report and family history alongside it is easy to misread. Bring what you find to a counsellor rather than acting on it alone.
Does the notation ever get corrected later?
The description of the change itself rarely changes once written correctly. What can change over time is how that change is classified, which is a separate line from the notation.
Who can actually explain my notation to me?
A genetic counsellor or clinical geneticist can walk through it line by line and connect it to what it means for you specifically. Call the helpline if you are not sure who to ask.
Your Specialists
Meet CION's oncologists. Bring your family history or genetic report to them.
Our medical oncologists see people with a strong family history of cancer, arrange genetic counselling and testing where it fits, and plan the checks that follow.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
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Sources
- GeneReviews (NCBI) — GeneReviews Overview
- MedlinePlus Genetics — What is a gene variant and how do variants occur?
- National Cancer Institute — Genetic Testing for Inherited Cancer Susceptibility Syndromes
- ClinVar (NCBI) — ClinVar: public archive of variant classifications
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
How to read a germline genetic test reportThe whole report, not just the notation lineWhat the gene name and transcript number meanThe reference map the notation is counted againstThe five variant classifications explainedWhat actually decides whether a change is harmfulClinVar and looking up your own variantWhere to check a notation safely, and how to read it there
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