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Aggregate size of a sextant biopsy core sample:

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In our practice, biopsy tissue core sizes vary by practitioner. Some produce 8 mm cores, and some produce 11-15 mm cores. At best, a core is only as thick or "fat" as 1 mm (the size of the lead in a refillable lead pencil). As calculated below, an exceptional sextant series of 6 cores from a 30 gram gland would only present a total of 0.2% of that prostate gland for processing and analysis under the microscope by the surgical pathologist. How can this be effective?

Prostate cancer has a strong tendency to crop up in several different sites within that gland, has a heavy tendency to arise in the edges (periphery) of the sides and back (toward the rectum) of the gland, and has a strong tendency to cause PSA to rise as it grows in quantity.

So, base-to-apex, spaced core biopsies taken through the rectum and aimed along the gland sides tend to "find" the cancer in cases of abnormally increased PSA test results. If the biopsy results are "negative" for cancer, you should continue to have your situation followed by a knowledgeable medical practitioner (usually a urologist) to see if (1) the DRE becomes abnormal or (2) the PSA continues to rise. This type of regular follow-up is, for us males, like the regular breast exams and mammograms and Pap smears are for females. Remember: negative biopsies do not guarantee that you are free of prostate cancer!


6 biopsy cores times 15 mm length per core=90 mm total aggregate length

length times cross-sectional surface area = volume

cross-sectional surface area = pie times radius squared=(3.14)(.5mm)(.5mm)=0.78 square mm

So, 90mm times 0.78 square mm= 70.2 cubic mm of biopsy tissue, total. (another source estimates that a sextant exam produces 150 cubic millimeters & that the volume of a typical prostate is 30,000 cubic millimeters).

A gram of prostate tissue measures exactly one cubic centimeter (1000 cubic mm).

Therefore, ([70.2 x 1/1000 x 1 g/cubic cm] divided by 30) x 100= 0.2% of gland taken out as biopsy cores!

Yet, the process is very effective at finding cancer in a patient's gland, especially if the pathologists are truly committed to finding the cancer if any be present in the core samples. As 2006 begins, we more often see 8-14 cores per case.

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(posted 11 December 1998; latest update 15 January 2006)