A Five-Day-Old Prostate Core and a Stain That Cannot Be Read
A paraffin block from an outside hospital arrives with a 1 mm prostate needle core and a note that the specimen was collected 5 days before processing. The in-house laboratory performs a p63/AMACR (P504S) double stain on a 4 micrometer section with EDTA pH 9 retrieval, 20 minutes at 100 C. The run's external control (a multitissue block containing known adenocarcinoma and benign glands) stains appropriately. On the patient's slide, basal cells show weak, patchy p63 nuclear staining in morphologically benign glands, and there is no AMACR staining in areas the H&E suggests are carcinoma. The section was cut 3 days before staining and stored at room temperature.
1. Can this slide be interpreted? Answer using the internal control, and state what a naive reading would get wrong.
Read the worked answer
No - the slide cannot be interpreted, and the reason is the internal control.
In a prostate double stain, the benign glands on the patient's own slide are the internal control: their basal cells must show crisp, continuous p63 nuclear staining. Here they are weak and patchy. Once the internal control underperforms, a negative AMACR result in the suspicious focus is uninformative - absent staining is equally consistent with "not carcinoma" and with "the epitope was not available."
The naive error is to read the combination as reassuring: weak p63 plus absent AMACR looks like "no basal cells, no cancer marker" and can be twisted into either a benign or a malignant call depending on what the reader expects. In fact both signals are degraded in the same direction, which is the signature of a technical failure, not biology.
Note the asymmetry: the external multitissue control performed well, but it is a different block with a different fixation history. It validates the reagents, not this core.
2. Rank the variables you would interrogate, and say what result would incriminate each.
Read the worked answer
Ranked by likelihood and by cost to test:
- Section age (cheapest to eliminate). A 4 micrometer section stored 3 days at room temperature can lose antigenicity, particularly for nuclear epitopes. Incriminating result: a freshly cut section from the same block stains crisply with no other change.
- Prolonged fixation. Five days in NBF for a 1 mm core is far beyond the ~24-48 hour optimum; over-crosslinking masks epitopes and typically produces exactly this weak, patchy nuclear pattern. Incriminating result: stronger staining after intensified retrieval (e.g., EDTA at pH 9 for 40 minutes, or a higher-temperature protocol) on a fresh section.
- Incomplete fixation or processing damage at the outside site - the mirror-image failure, which can also give weak staining and poor morphology. Incriminating result: pale, hazy morphology on H&E plus weak staining that does not respond to longer retrieval.
- Retrieval/detection shortfall for this particular block. Incriminating result: graded improvement as retrieval time is extended, judged against the patient's own benign glands.
- Antibody clone performing poorly on this tissue. Test last; it is the most expensive change and now rare with a validated clone.
Test in that order because items 1 and 2 are cheap and account for most failures.
3. What do you report, what do you tell the pathologist, and what system change prevents a repeat?
Read the worked answer
Report: state that the immunostain is non-contributory because the internal control failed, and that the case is being repeated. Do not issue a report in which a negative AMACR is presented as evidence against carcinoma - that is the specific harm here.
To the pathologist: name the failure mode (internal control weak in benign glands), the suspected cause (5-day fixation, plus a 3-day-old section), the plan (fresh section, intensified retrieval, re-run with the patient's benign glands used as the on-slide control), and the fallback (a different marker or a second opinion on the block if the repeat fails). If the case is a consult, saying explicitly "this stain cannot be interpreted" is more useful than silence.
System changes:
- Request blocks, not slides, from outside institutions, and cut fresh sections in-house.
- Record and transmit fixation time. A stated collection-to-processing interval should trigger a documented retrieval adjustment, not a routine run.
- Cut and stain on the same day for nuclear markers; write a maximum section age into the SOP.
- Define the internal control requirement in the stain SOP - the run is rejected for that block when the on-slide control fails, and the rejection is logged so repeat rates become a monitored indicator.