Paraffin Block

A paraffin block is a small block of wax holding a piece of tissue removed during a biopsy, surgery or autopsy. The tissue is preserved in formalin, embedded in paraffin, and thin slices are cut from it to make slides. The blocks are the lasting physical record of a diagnosis and are often the most important medical evidence in an asbestos case.

Origin

Embedding tissue in paraffin wax to cut thin sections became standard in the late nineteenth century and remains the basis of surgical pathology. Formalin-fixed, paraffin-embedded tissue can be kept for decades and still be used for many stains and genetic tests.

Significance in Asbestos Context

Slides can be recut from a block for second opinions, new immunostains, BAP1 or MTAP testing, genetic studies of the tumor and, for lung tissue, asbestos body counts or fiber burden analysis. In litigation, both sides' experts often want to review or test the tissue. Hospitals keep blocks for a set period, often at least ten years under common accreditation rules, and may discard them afterward, so preserving them early matters, especially if the patient has died. Releasing blocks usually requires written authorization from the patient or the estate's representative and is often limited to recut slides or small portions so the hospital keeps some tissue. Testing that uses up tissue should be agreed in advance, because destroying evidence can lead to court disputes. Once a block is gone, it cannot be replaced.

Example Sentence

The lawyer sent the hospital a preservation letter and a signed authorization so that the 2019 pleural biopsy blocks could be recut for an independent pathology review.

Related Terms

Pathology Report, Pathology Review, Chain of Custody, Spoliation, Fiber Burden Analysis, Immunohistochemistry, Cell Block, Autopsy

Notes

• Ask your lawyer to send a preservation request for all blocks and slides as soon as possible.
• Write down every hospital and lab where a biopsy or surgery was done; blocks may be in several places.
• Do not agree to any testing that uses up the tissue without talking to your lawyer first.