Prostate needle biopsy samples
Prolaris testing only requires a small amount of quality tumor in order to run the test
If you are submitting a sample from a prostate needle biopsy please include 7 consecutive slides, each 3-5 microns in thickness with tumor that is at least 0.5mm in length.
Several factors can affect the quality of the sample:
- Number of positive cores
A greater number of positive cores increases the likelihood of sample acceptance, since tumor can be combined from multiple cores. With a single positive core, sample acceptance is most correlated with the percentage of tumor in the core (the higher the % the more likely the acceptance).
- Percentage of core that is positive
Cores with less than 10% involvement may not meet the 0.5mm in length requirement. This can be fixed by combining tumor from multiple cores. (cores range in length from 5 mm to 15mm).
- Tissue remaining in the block
The procedure for cutting tumor sections to diagnose cancer varies greatly by pathology lab.
- Labs vary in how deeply they face the block. These initial sections are all discarded.
- Most labs cut between 2 and 6 levels. The greater the number of levels cut, the smaller the amount of tissue remaining in the block.
- Many labs discard the intervening sections between the sections they use for diagnosis.
- The percentage of the core remaining after slides are cut for diagnosis varies from 0% (no tissue) to 50%.
- Quality of sample
In addition to 0.5mm in length, samples must also contain 75% or greater tumor glands of macro dissectible tumor tissue. Often prostate needle biopsies contain small foci of invasive cancer intermixed with normal tissue, which makes macro dissection of tumor difficult. The sample must be fixed in a formalin based fixative.
The sample must be fixed in a formalin based fixative.