How Histopathology Confirms a Cancer Diagnosis — What Pathologists Look For
The Microscope as the Final Arbiter of Diagnosis
In cancer medicine, no investigation carries more weight than the histopathology report. A CT scan can show a mass. An MRI can characterise its behaviour. A tumour marker can raise suspicion. But none of these investigations confirms cancer with the certainty that microscopic tissue examination provides. The pathologist examining a stained tissue section under the microscope is performing the investigation that decides whether a patient has cancer, what type it is, how aggressive it is, and what treatment it requires. Understanding what the pathologist looks for — and how they reach their conclusions — gives patients and families insight into the science behind their most important diagnosis.
At Alnoor Diagnostic Centre in Shadman, Lahore, our histopathology laboratory provides expert tissue examination and pathological reporting that clinicians across the city depend on for accurate cancer diagnosis and treatment planning.
What Normal Tissue Looks Like — The Baseline for Comparison
To understand how a pathologist identifies cancer in a tissue section, it is essential to first understand what normal tissue looks like under the microscope. Normal tissues have a highly organised, predictable architecture that reflects their function. The normal colonic mucosa, for example, shows neatly arranged glands of uniform size lined by orderly cells with round, basally positioned nuclei — all oriented in the same direction, all dividing in a controlled manner at specific locations, all maintaining a consistent relationship to each other and to the surrounding supporting tissue.
This orderliness is the fundamental characteristic of normal tissue. Cells know their place, they reproduce only when needed, they maintain their structural specialisation, and they respect the boundaries that separate one tissue compartment from another. Cancer is, at its most fundamental level, a disruption of this orderliness — a breakdown of the regulatory mechanisms that maintain normal tissue architecture and cell behaviour.
The pathologist’s task is to identify these disruptions, characterise their nature, and determine whether they represent cancer, a pre-malignant condition, or a benign abnormality.
The Core Features of Malignancy — What Pathologists Identify
Abnormal nuclear morphology — The nucleus of a cell contains its genetic material and is the most informative structure a pathologist examines when assessing for malignancy. Normal cells have nuclei of consistent size with smooth, regular outlines and finely dispersed chromatin. Cancer cells typically show a constellation of nuclear abnormalities that together constitute the microscopic signature of malignancy.
Nuclear enlargement — nuclei that are significantly larger than those of normal cells in the same tissue — is one of the most consistent features of malignancy. The nuclear-to-cytoplasmic ratio increases, meaning the nucleus occupies a disproportionately large fraction of the cell volume. Nuclear pleomorphism — variation in nuclear size and shape between cells in the same tumour — reflects the genetic instability of malignant cells. Nuclear hyperchromasia — darker staining of the nucleus from increased DNA content — is another characteristic feature. Prominent nucleoli — the dark structures within nuclei responsible for ribosome production — are enlarged and conspicuous in many carcinomas, reflecting the intense metabolic activity of rapidly dividing cancer cells.
Nuclear membrane irregularity — irregular, angular, or notched nuclear outlines rather than the smooth oval of normal nuclei — reflects chromosomal abnormalities within the cancer cell. The pathologist assesses all these nuclear features simultaneously, building a composite picture of nuclear atypia that informs the overall assessment.
Increased and abnormal mitotic figures — Cell division — mitosis — is visible under the microscope as a specific sequence of nuclear changes that are recognisable at each stage. Counting mitotic figures per unit area of tissue provides a direct measure of how rapidly the tumour cells are dividing. Normal tissues have very few visible mitoses because division is carefully regulated and infrequent. Most malignant tumours show increased mitotic activity — higher numbers of dividing cells per field — reflecting uncontrolled proliferation.
Even more diagnostically significant than increased mitotic count are abnormal mitotic figures — divisions in which the chromosomes are segregated abnormally, producing bizarre multi-polar or asymmetric mitotic patterns that are almost never seen in normal tissue. Abnormal mitoses are highly specific for malignancy and carry prognostic significance in several tumour types.
Loss of normal tissue architecture — Normal tissue architecture is the organised arrangement of cells into functional units — glands, ducts, lobules, or other structures — that reflects the specialised function of that tissue. Malignant tumours disrupt this architecture in characteristic ways that reflect the degree of differentiation — how closely the tumour cells resemble their normal counterparts.
Well-differentiated carcinomas — those of lower histological grade — retain recognisable architectural features of their tissue of origin. A well-differentiated adenocarcinoma of the colon still forms glands, but they are irregular in shape, size, and orientation compared to normal colonic glands. Poorly differentiated carcinomas — higher grade — have largely lost their architectural similarity to normal tissue, with cells growing in solid sheets, nests, or cords without forming recognisable functional structures. Undifferentiated or anaplastic tumours show so little resemblance to normal tissue that their cell of origin cannot be determined from H&E staining alone without immunohistochemistry.
Invasion — One of the most definitive features of malignancy is invasion — the ability of tumour cells to penetrate through the tissue boundaries that contain normal cells. In the transition from a pre-malignant lesion to frank carcinoma, the critical event is the breach of the basement membrane — the thin protein layer that normally separates surface epithelium from the underlying connective tissue stroma.
A carcinoma-in-situ has all the cellular features of malignancy but has not yet breached the basement membrane. When malignant cells penetrate through the basement membrane into the surrounding stroma — invasive carcinoma — they have acquired the capacity to spread to lymph nodes and distant sites. Identifying invasion is therefore one of the most clinically significant determinations a pathologist makes from a tissue section.
Lymphovascular invasion — the presence of tumour cells within blood vessels or lymphatic channels — indicates that the cancer has already begun its journey toward distant spread. Its presence on histopathology carries direct prognostic significance and influences staging, adjuvant treatment decisions, and follow-up intensity.
Perineural invasion — tumour cells growing along nerve sheaths within the tissue — is associated with higher recurrence risk and more aggressive behaviour in several tumour types including prostate, pancreatic, and colorectal carcinoma.
Histological Grading — Quantifying Aggressiveness
Once malignancy is confirmed, the pathologist assigns a histological grade that reflects the degree of differentiation and aggressiveness of the tumour. Different tumour types use different grading systems, but the fundamental principle is consistent — well-differentiated tumours that closely resemble normal tissue tend to behave less aggressively than poorly differentiated tumours that have largely lost their resemblance to their tissue of origin.
In breast cancer, the Nottingham grading system scores three features — tubule formation, nuclear pleomorphism, and mitotic count — each on a one to three scale, producing a combined score that determines whether the tumour is grade one, two, or three. Grade one breast cancers tend to be slow-growing with a more favourable prognosis. Grade three cancers are fast-growing and more likely to metastasise.
In colorectal cancer, glandular differentiation determines grade — well-differentiated tumours form glands in more than ninety-five percent of the tumour, poorly differentiated tumours in less than fifty percent. In prostate cancer, the Gleason grading system assigns a pattern score from one to five to the two most predominant architectural patterns, whose sum produces the Gleason score that drives management decisions.
Grade is reported alongside diagnosis in every cancer pathology report because it directly influences treatment selection, adjuvant therapy decisions, and prognostic estimation.
Immunohistochemistry — Characterising the Tumour Beyond H&E
When H&E examination establishes that a malignancy is present but additional characterisation is needed — to determine the tissue of origin, classify the tumour subtype, identify specific therapeutic targets, or assess prognostic markers — immunohistochemistry is applied to additional sections from the paraffin block.
Immunohistochemistry uses specific antibodies to identify proteins expressed within tumour cells, providing a molecular fingerprint that characterises the tumour beyond what morphology alone can reveal. A metastatic adenocarcinoma with unknown primary site expresses a specific panel of proteins — TTF-1 and napsin-A positivity indicates lung origin, CK20 and CDX2 positivity indicates colorectal origin, PAX-8 indicates renal or gynaecological origin — each combination directing further clinical investigation toward the likely primary tumour.
In breast cancer, oestrogen receptor, progesterone receptor, and HER2 immunohistochemistry determine the molecular subtype of the tumour — luminal A, luminal B, HER2-enriched, or triple-negative — with direct implications for treatment. Hormone receptor positive tumours respond to endocrine therapy. HER2-positive tumours respond to trastuzumab and pertuzumab. Triple-negative tumours require chemotherapy. These treatment decisions — each carrying significant clinical and financial implications — are driven by immunohistochemical results from the pathology specimen.
In lymphoma, a panel of lymphoid markers — CD20, CD3, CD10, BCL2, BCL6, MUM-1, and others — classifies the lymphoma into its specific subtype with the precision that determines whether treatment will be CHOP chemotherapy, targeted biological agents, stem cell transplantation, or a watch-and-wait approach. Without immunohistochemistry, lymphoma subclassification from H&E alone is impossible in most cases.
The Final Pathology Report — What It Tells the Treating Clinician
The histopathology report that emerges from this complete process is a structured clinical document that provides the treating oncologist, surgeon, or specialist with everything needed to make treatment decisions. It states the diagnosis — the tumour type and subtype — the histological grade, the tumour dimensions, the lymphovascular and perineural invasion status, the resection margin status confirming whether the tumour was completely excised or whether malignant cells are present at the edge of the surgical specimen, and the results of all immunohistochemical studies. For surgical specimens, nodal involvement is documented — how many lymph nodes were examined and how many contain tumour deposits — providing the staging information that determines systemic treatment need.
Every element of this report translates directly into a clinical action — the grade determines adjuvant chemotherapy intensity, the margin status determines whether re-excision is needed, the receptor status determines targeted therapy eligibility, the nodal status determines systemic treatment requirement and prognosis.
Histopathology at Alnoor Diagnostic Centre, Lahore
At Alnoor Diagnostic Centre in Shadman, Lahore, our histopathology laboratory provides expert tissue processing, comprehensive staining including immunohistochemistry, and thorough pathological examination by experienced pathologists. Every specimen received at our laboratory is examined with the rigour and clinical relevance that cancer diagnosis demands — because every report we issue informs a decision that matters profoundly to a patient and their family.