Cells and tissues are analyzed in the laboratory to look for the presence or effects of diseases, including cancer. Cells may be collected from samples of body fluid (such as urine or blood), with needle aspiration or by scraping them from the surface of organs. Tissue samples may be collected through biopsy or during endoscopic procedures.
- Cytology refers to the study of cells, including origin, structure, function and signs of disease.
- Cytopathology refers to the analysis of cells.
- Histopathology refers to the analysis of tissues.
Why cell and tissue studies are done
Cell and tissues studies are done to:
- see what types of cells are present based on their appearance and characteristics
- screen for precancerous conditions
- diagnose cancer
- identify cancer type, the degree of aggressiveness and possible spread of the cancer
- monitor the response to treatment
How cell and tissue samples are collected
Tissue or cell samples can be removed from practically any part of the body, such as:
- organs or structures (for example, breast, prostate, lung, thyroid, liver, stomach or colon)
- lymph nodes
- bone marrow
- other body fluids (urine, cerebrospinal fluid, fluid in the lungs or abdomen)
The procedure used to collect a cell or tissue sample depends on the type of cancer suspected and the part of the body affected. The most common procedures are:
How cell and tissue studies are done
The cells or tissue samples are sent to the laboratory so they can be examined under a microscope by a cytologist or pathologist. Complex analytical methods, such as flow cytometry or molecular genetics, may also be used for special studies.
Special laboratory techniques are used to prepare the samples so they can be viewed under a light microscope, fluorescent microscope or electron microscope. The preparation and special microscopes allow the cytologist or pathologist to see very small details in cells.
- cytochemistry and histochemistry
- Special stains are used to identify cell and tissue structures based on their chemical properties.
- The staining pattern is examined using a microscope.
- immunohistochemistry and immunofluorescence
- These techniques use a very specific antigen-antibody reaction to identify proteins in tissues or cells.
- Monoclonal antibodiesMonoclonal antibodiesA substance that can find and bind to a particular target molecule ( antigen) on a cancer cell. linked with a fluorescent or specific enzyme label are used. They will bind only to specific antigens (proteins). The fluorescent or enzyme label allows the cells to be visualized and detected.
- A microscope is generally used to view these reactions and allows the pathologist to examine the cells along with details of their surroundings.
Flow cytometry is more informative than immunofluorescence because many special antibodies can be viewed at the same time. It is less labour intensive because of automation but requires very complex equipment. A laser is used to examine cells one at a time. They are identified and counted based on the immunofluorescent tag bound to their surface protein.
The advantage of this method is that it allows data to be collected rapidly from thousands of cells in a single sample. The results are then analyzed by a computer. A drawback to this method is that details of the cell’s surroundings cannot be examined because tissue needs to be broken down into single cells.
Both microscopy methods and flow cytometry can be used to find:
- the types of cells present and their degree of abnormality (size and shape of cell and its nucleus)
- the hormone receptor status of individual cells (such as estrogen and progesterone receptors in breast tissue)
- tumour markertumour markerA substance in the body that may indicate the presence of a certain type of cancer. proteins (such as PSA)
- expression of cellular oncogenesoncogenesA gene involved in the control of cell growth and division that may cause the growth of cancer cells. (such as ERBB2, more commonly known as HER2)
- expression of specific cell surface proteins (such as CD19) that are markers for cell types or degree of maturation
- altered expression of suppressor genessuppressor genesA gene normally found in the body that helps control cell growth and may help limit the growth of cancer cells. (such as TP53)
Microscopy methods and flow cytometry also allow the pathologist to see different aspects of the cells.
- the size, shape and structure (morphology) of tissue
- the general appearance of cells
- the degree that malignant cells differ from normal cells (grading)
- flow cytometry
- light scatter characteristics
- the DNA content of malignant cells
Molecular genetic methods
Molecular genetic methods are used to study abnormalities in chromosomes (the part of a cell that contains genetic information) or the DNA of cells. These methods will identify changes to the chromosomes and genes, such as duplications, translocations, mutations and deletions.
Cytogenetic tests (chromosome analysis)
Chromosome analysis looks for changes to a person’s chromosomes. Karyotyping and fluorescent in situ hybridization (FISH) are cytogenetic tests that may help diagnose some cancers.
- A karyotype is a picture of a person’s chromosomes. It is obtained by staining the chromosomes to create an alternating black and white pattern called chromosome banding.
- This technique helps to identify and distinguish segments of individual chromosomes (like bar codes).
- The karyotype is used to screen for chromosomal abnormalities, such as:
- an additional chromosome or an extra part of a chromosome (duplication)
- a missing chromosome or part of a chromosome (deletion)
- rearranged or translocated chromosomes where parts of 2 chromosomes are exchanged (for example, the t(9;22) translocation, known as the Philadelphia chromosome, helps diagnose chronic myelogenous leukemia)
- fluorescent in situ hybridization (FISH)
- FISH is used to identify chromosomal abnormalities and other genetic changes in cells using special DNA probes labelled with fluorescent dyes.
- This method allows the pathologist to see:
- similar findings as for karyotyping but with increased accuracy
- extra copies of oncogenes that can develop in some cancers (for example, HER2)
Polymerase chain reaction (PCR)
PCR is a specific molecular genetic method used to produce many copies of a particular gene segment. This allows the pathologist to do more extensive laboratory studies.
PCR is a very sensitive technique that can be useful in diagnosing leukemia, lymphoma and solid tissue cancers in cases where only a small number of cancer cells are present. It can also be used during follow-up after treatment to see if the cancer is gone.
What is reported in the results
All the findings and results lead to a pathology report that can include:
- gross (macroscopic) description – a description of the sample as seen with the naked eye (for example, the size of the tumour)
- microscopic description – a description of the sample as it looks under a microscope (for example, the appearance and behaviour of the cells and if they are normal cells or cancer cells)
- This descriptions might also include:
- how fast the cells are multiplying
- the extent that the cancer cells invade nearby tissue, blood vessels or lymph vessels
- how close the cancer is to the edge of the surgical margin (the area of normal tissue around the tumour)
- information from special tests, such as microscopy, flow cytometry or molecular genetics
- a diagnosis that describes the type of cancer, type of cell the cancer developed from, grade and extent of spread (stage)
The doctor will then decide if more tests, procedures, follow-up or additional treatments are needed.
Note: Other techniques or studies can be done. Only the main cancer-related ones have been included here.