Whole-mount pathology

Whole-mount pathology, also called large format histology or whole-mount sectioning, is the examination of tissue sections cut from specimens processed in large tissue cassettes, so that a complete cross-section of the organ sits on a single slide. In prostate cancer it is applied to the radical prostatectomy specimen. A collaborative review of the literature found that whole-mount sections are not superior to standard sections at detecting adverse pathological features, and that their advantage is spatial: they display the architecture of the gland and identify and locate tumour nodules, and the index tumour in particular, more clearly, which makes the pathology far easier to compare with the digital rectal examination, the transrectal ultrasound, the multiparametric magnetic resonance imaging, the operation and the biopsies.

That is why it is the reference standard for imaging accuracy. Johnson and Raman co-registered multiparametric magnetic resonance imaging with whole-mount pathology in 588 consecutive men who had a 3 Tesla scan before radical prostatectomy, giving 1,213 pathologically confirmed tumour foci, and measured per-lesion rather than per-patient sensitivity. The scan detected 45 percent of all foci (95 percent confidence interval 42 to 47) and 65 percent of clinically significant lesions (61 to 69), and missed at least one clinically significant focus in 34 percent of men overall and 45 percent of men with multifocal disease. Set against PROMIS's 93 percent per-patient sensitivity for clinically significant cancer, the gap of roughly 30 percentage points is the difference between asking whether a man has a serious cancer and asking where all of it is, and it is precisely the territory in which focal therapy and imaging-only surveillance operate.

The method has limits of its own. Co-registration of a scan with a whole-mount section is imperfect, which biases measured detection downwards by an unknown amount; the specimen shrinks and deforms in processing; a prostatectomy cohort is enriched for intermediate and high-risk disease and cannot report specificity; and standardised annotation protocols show excellent agreement between pathologists for cancer localisation and grading but persistent variability for cribriform growth and intraductal carcinoma.