Flow Cytometry and the Diagnosis of Lymphomas and Leukemias

Claudia McNabbTHUNDER BAY – Healthbeat – It may sound obvious, but to treat cancer effectively you first have to identify exactly what type of cancer it is.

For example, when you talk about disorders like leukemia and lymphoma (malignancies of the blood, bone marrow and/or lymph nodes) you’re actually talking about a group of cancers, each with its own unique signature – and its own treatment.

“In the past, diagnosis relied greatly on studying cells under a microscope, where classification was difficult,” said Georgia Carr, Coordinator of Flow Cytometry and of Quality and Compliance of the Clinical Laboratory at the Thunder Bay Regional Health Sciences Centre. “With flow cytometry, we are now doing a better job at pinpointing disease. It helps us determine the disease ‘thumbprint’ so that the patient can receive a more specific treatment having a much better chance of recovery.”

Flow cytometry uses a combination of biology, physics, math, and computer science to help the pathologist with diagnosis. The process itself is complex (please see “What is Flow Cytometry?” on this page) but is essentially the sorting of white blood cells or “leukocytes”.

As most people know, white blood cells are responsible for fighting off disease in the body. They carry “antigens” (short for “antibody generators”), and it is these antibodies that attack invading organisms.
There are consistent numbers and types of antigens for each kind of leukocyte at each stage of its growth. But in leukemia and lymphoma, cells may not mature and/or they may display an abnormal number or combination of antigens. Flow cytometry identifies these antigens.

Flow ChartsDepending on the cancer suspected, a blood, bone marrow, or lymph node sample is collected from the patient and sent to Laboratory Services at the Health Sciences Centre. There the white blood cells are separated and mixed with an array of “fluorochrome-labelled” antibodies, which attach to corresponding leukocyte antigens, if present. This mixture is then introduced to a flow cytometer (cell sorter) where cells pass single-file through a laser light beam. If attached to a cell, the fluorochromes emit different colours (fluorescence).

Healthy cells fluoresce in normal amounts and patterns while cancerous cells do not. Interestingly they do display unique signatures according to type, though there are exceptions.

“That’s the thing about disease, not everything goes according to plan – cancer cells do not read text books. All we can do is provide the pathologist with our data as a piece of the puzzle,” said Carr.

The way that data is interpreted is vitally important. It isn’t a pass/fail test – 10,000 or more cells are examined from each specimen and the results are graphed where percentages and patterns are calculated and interpreted. It’s for this reason Flow Cytometry Technologists work closely with pathologists and oncologists.

“Working as a flow cytometrist requires highly specialized training,” Carr said. “But cancer diagnosis is a team-based approach, where haematologists, oncologists, pathologists, nurses, medical laboratory technologists and booking clerks all deserve a lot of credit.”

Flow cytometry can be used for other tests; at the Health Sciences Centre, flow cytometry is also used to track T-cells during treatment of HIV positive patients. However the vast majority of tests – hundreds per year – are for blood-borne cancers.

“I’m proud that the Health Sciences Centre has a Flow Cytometry department,” Carr said. “The test takes approximately three hours from start to finish, so results can be ready same day. That can be a real bonus when a malignancy such as an acute leukemia is found, because the faster the patient can get treated, the better the outcome. I can’t imagine life without flow!”

Graham Strong

In the top photograph: Claudia McNabb, Medical Laboratory Flow Cytometry Specialist, analyzing data. The flow cytometer or “cell sorter” was purchased in part thanks to a grant from the Thunder Bay Regional Health Sciences Foundation.