The pathology report is the document that describes what the pathologist saw under the microscope after examining the tissue from your biopsy or surgery. It is dense, technical, and written for other doctors. It is also the single most important piece of paper in your cancer file. Every subsequent decision — whether you need surgery, what kind of chemotherapy to give, whether targeted or hormonal therapy makes sense, whether immunotherapy is an option — is built from the information on this page.
Most patients receive their report and understand only the headline ("it's cancer"). The rest is mostly skipped. That's a missed opportunity. The report contains the answers to questions you'll otherwise be asking your oncologist for months. Knowing how to read it lets you participate in treatment decisions instead of just nodding along.
This is a plain-English guide to the parts of the report most patients ask about, in roughly the order they appear.
1. The diagnosis line
The top line of the report tells you the cancer type. This will use medical names — "invasive ductal carcinoma" for the most common breast cancer, "adenocarcinoma" for lung and colon cancers, "squamous cell carcinoma" for many head-and-neck cancers, "high-grade serous carcinoma" for the most common ovarian cancer.
The two pieces of the diagnosis matter:
- Cell type — what kind of cell the cancer started from. This shapes the treatment menu more than almost anything else.
- "Invasive" vs "in situ" — this distinction matters enormously. "In situ" means the cancer is still confined to the layer of cells where it started; it has not crossed the basement membrane. In situ disease (ductal carcinoma in situ in breast, carcinoma in situ in cervix, melanoma in situ in skin) is far more treatable and often considered pre-cancer. Invasive disease has crossed that line and is the entity we usually mean when we say "cancer."
2. Differentiation and grade
"Grade" describes how abnormal the cancer cells look under the microscope compared to normal cells of that tissue. The pathologist is essentially asking: does this still look like the tissue it came from?
- Well-differentiated (Grade 1, low grade) — cells still look fairly normal. Generally slower-growing, better prognosis.
- Moderately differentiated (Grade 2) — middle ground.
- Poorly differentiated (Grade 3, high grade) — cells look chaotic, no longer resemble the original tissue. Generally faster-growing, more aggressive, often warrants more intensive treatment.
For some cancers, the grading system is named: prostate cancer uses the Gleason score (6 = lowest grade, 10 = highest); some cancers use Nottingham grade for breast; sarcomas have their own systems. The number means the same thing across systems: higher number = more aggressive-looking cells.
3. Tumour size and stage
Size is given in centimetres or millimetres in two or three dimensions. This matters because size correlates with stage, and stage drives treatment. Most cancers use the TNM staging system:
- T (tumour) — the size and local extent of the primary tumour. Higher T = larger or more locally invasive.
- N (nodes) — whether and how many regional lymph nodes contain cancer. N0 = no nodes positive. N1, N2, N3 = increasing involvement.
- M (metastasis) — whether cancer has spread to distant organs. M0 = no, M1 = yes.
The combined TNM is then converted to an overall stage from I to IV. A localised cancer might be stage I or II. Regional spread (to nearby lymph nodes) often means stage III. Distant spread (to lung, liver, bone, brain) is stage IV.
Staging on a biopsy alone is incomplete — the report from a small needle biopsy can't tell you about lymph node spread or distant spread. Final staging usually requires either surgical pathology (after excision) or staging scans (CT, MRI, PET).
4. Margins
For surgical specimens, the report tells you whether the cancer extends to the edges of the tissue removed:
- Negative margins — no cancer at the edges; a rim of normal tissue surrounds the cancer. Good news.
- Close margins — cancer is near the edge but not touching it. May or may not warrant additional treatment.
- Positive margins — cancer cells extend to the cut edge. Often means the surgeon didn't get all the cancer. Usually requires further surgery, radiation, or both.
The exact margin distance matters. A 2mm margin is interpreted differently in different cancers and centres. Ask your surgeon and oncologist to explain what the margin distance means in your specific case.
5. Lymphovascular invasion (LVI) and perineural invasion (PNI)
These describe whether the pathologist saw cancer cells inside small blood or lymph vessels (LVI) or wrapped around small nerves (PNI) within the tumour or its surroundings. Both are markers that the cancer has begun to spread microscopically. They don't necessarily mean cancer has reached distant sites, but they upgrade the risk of recurrence and often shift treatment toward more aggressive adjuvant therapy.
6. Immunohistochemistry (IHC) markers
IHC is a staining technique that detects specific proteins on cancer cells. These markers shape treatment:
For breast cancer
- ER (oestrogen receptor) — positive vs negative; reported as a percentage of cells positive (e.g., "ER positive, 90%"). ER positive cancers respond to hormonal therapy.
- PR (progesterone receptor) — same convention. PR-positive often supports the prognosis already implied by ER-positive.
- HER2 — reported on a 0 to 3+ scale. 0 and 1+ are negative. 3+ is clearly positive (treat with anti-HER2 therapy). 2+ is "equivocal" and needs a confirmatory FISH or other in-situ hybridisation test.
- Ki-67 — a proliferation marker, reported as a percentage. Higher Ki-67 = more dividing cells = more aggressive cancer in general. The threshold for "high" varies (often 14-20%).
For lung cancer (NSCLC)
- PD-L1 — reported as a percentage (TPS, tumour proportion score). High (≥50%) qualifies for first-line single-agent immunotherapy. Lower scores still allow combination immunotherapy + chemotherapy.
- EGFR, ALK, ROS1, KRAS, BRAF, MET, RET, NTRK, HER2 — usually tested by molecular methods (NGS or PCR), not IHC, but increasingly co-reported. Each enables a specific targeted therapy.
For colorectal cancer
- MSI / MMR — microsatellite instability or mismatch repair status. MSI-high or dMMR (deficient mismatch repair) qualifies for immunotherapy. About 15% of colorectal cancers.
- KRAS, NRAS, BRAF, HER2 — guides targeted therapy choice in advanced disease.
The list is different for every cancer. The principle is the same: each marker enables (or rules out) a specific treatment.
Every subsequent decision — surgery, chemo, hormonal, immunotherapy — is built from this page.
7. Molecular / genomic testing
For most modern cancer diagnoses, the IHC panel is now combined with — or upstreamed by — molecular testing using next-generation sequencing (NGS). This tests dozens to hundreds of cancer-related genes simultaneously, looking for actionable mutations.
Common reportable findings:
- Driver mutations — single-gene changes that drive the cancer's behaviour. EGFR in lung, BRAF in melanoma and colon, KRAS G12C in lung, BRCA in breast/ovarian/prostate.
- Tumour mutational burden (TMB) — overall load of mutations. High TMB is a positive predictor for immunotherapy response in many cancers.
- Microsatellite instability (MSI) — covered above.
- Homologous recombination deficiency (HRD) — relevant in ovarian cancer and increasingly in others. Predicts PARP-inhibitor response.
- Fusions and rearrangements — gene fusions like ALK-EML4 in lung, NTRK fusions across cancers, BCR-ABL in leukaemia. Each enables specific targeted therapies.
8. Specimen comments and pathologist's note
Many reports include a free-text comment section at the end. This is where the pathologist captures things that don't fit the structured fields — uncertainty about a finding, recommendations for additional testing, comparisons to prior biopsies, and so on. Read this section carefully. It often contains the most clinically actionable details and the pathologist's honest assessment of any ambiguity.
What to ask your oncologist about your report
Bring the full report to your consultation. The questions that yield the most are:
- What is the diagnosis (cell type and invasive vs in situ)?
- What is the grade or differentiation?
- What is the stage, and what scans do I need to confirm it?
- What are my margin status and lymphovascular invasion findings?
- What IHC markers were tested? What do my results mean for treatment?
- Was molecular / NGS testing done? If not, should it be?
- Are there findings that warrant a pathology re-read at another centre — especially for rare or ambiguous cancers?
The last question is worth asking explicitly. Pathology re-read at a high-volume reference centre changes the diagnosis or staging in approximately 5-10% of cases of unusual cancers — sometimes meaningfully. Second opinions often start with a pathology re-read.
The summary
Your pathology report is technical for a reason: it carries the precise information needed to plan your treatment. Diagnosis, grade, stage, margins, vascular and nerve invasion, IHC markers, and molecular results — each of these has a specific role in shaping what comes next. You don't need to memorise the language. You do need to know that every line on this page matters, and that asking your oncologist to walk you through it is one of the highest-yield conversations you can have. The report is the map. Treatment is the route. Understanding the map makes the route make sense.