Cell Block

A cell block is a small paraffin block made from cells spun out of pleural fluid, ascites or a needle aspirate. It lets the lab cut thin slices of fluid cells just as it would tissue, so immunostains and molecular tests can be run on them. It is often the key to diagnosing mesothelioma from fluid.

Origin

Laboratories have made cell blocks from body fluids for many decades as a way to treat loose cells like tissue. Their importance grew as immunohistochemistry and molecular testing became central to diagnosing mesothelioma and lung cancer.

Significance in Asbestos Context

Many people with pleural mesothelioma first have fluid drained from the chest, and the fluid may contain tumor cells. A smear alone can be hard to interpret, but a cell block lets the pathologist run a panel of stains, such as calretinin, WT-1 and keratins to identify mesothelial cells, markers to rule out lung, breast or ovarian cancer, and BAP1 or MTAP to look for signs of malignancy. Some guidelines accept a fluid-based diagnosis of mesothelioma when these tests are convincing, though a tissue biopsy is still often recommended. The cell block is also a lasting record: it is stored like a tissue block and can be re-tested later, including by experts on both sides of a case. If a lab did not make a cell block, it may not be possible to go back and make one.

Example Sentence

The pleural fluid cell block was positive for calretinin and WT-1 and showed loss of BAP1, supporting a diagnosis of mesothelioma.

Related Terms

Fluid Cytology, Cytology, Paraffin Block, Immunohistochemistry, Calretinin, BAP1, Pleural Effusion, Thoracentesis

Notes

• When fluid is drained, ask whether it will be sent for cytology with a cell block.
• Ask the lab to keep cell blocks and slides; they can be needed years later.
• Your lawyer may ask the lab to preserve these materials formally.