Diastase-Periodic Acid Schiff (PAS) Method

A two-step histology stain in which tissue is first treated with the enzyme diastase to digest away glycogen, then stained with Periodic Acid–Schiff reagent, which turns carbohydrate-rich structures bright magenta. Comparing the diastase-treated slide to an untreated PAS slide tells the pathologist which magenta material was glycogen and which was a non-glycogen carbohydrate such as mucin. In thoracic pathology it is used mainly to help distinguish mucin-producing adenocarcinoma from mesothelioma.

Origin

Periodic acid–Schiff staining was introduced by McManus and by Hotchkiss in 1946–1948, building on the Schiff reagent developed by German chemist Hugo Schiff in 1866. Adding a diastase (amylase) digestion step as a control for glycogen became a standard variant shortly afterward and is now routine in surgical pathology.

Significance in Asbestos Context

For patients whose biopsy is being evaluated for mesothelioma, the diastase-PAS stain is one of the classic tools used to rule out adenocarcinoma of the lung, which can look very similar under the microscope. Adenocarcinoma cells often contain neutral mucin that stays magenta after diastase digestion ("diastase-resistant PAS-positive"), while mesothelioma cells typically do not. A confident mesothelioma diagnosis frequently depends on this kind of differential staining, alongside modern immunohistochemistry panels (calretinin, WT-1, CK5/6, BAP1, claudin-4, MOC-31). Because the cancer's identity directly affects treatment options, prognosis, and the legal claim, the stains noted in your pathology report matter.

Example Sentence

The pathology report noted that the tumor cells were negative on diastase-PAS, which, combined with positive calretinin and WT-1 staining, supported the diagnosis of epithelioid mesothelioma rather than metastatic adenocarcinoma.

Related Terms

Immunohistochemistry, Mesothelioma, Adenocarcinoma, Mucicarmine Stain, Histopathology, Differential Diagnosis

Notes

• Request a complete copy of your surgical pathology report and ask whether diastase-PAS (often written "PAS-D" or "PASD") and a full mesothelioma immunohistochemistry panel were performed; if not, ask whether the paraffin tissue blocks can be sent for additional stains or expert review.
• For a suspected mesothelioma diagnosis, consider asking your treating physician about a second opinion from a mesothelioma reference center (such as a U.S. Mesothelioma Applied Research Foundation–affiliated program or a major academic cancer center); these centers routinely re-cut and re-stain the original blocks.
• Preserve the original pathology slides and paraffin blocks. They are the single most important physical evidence in both your medical care and any legal claim, and hospitals may discard or release them only on written request.
• Diastase-PAS alone cannot diagnose asbestos exposure or asbestosis; it is a tissue-typing stain used to identify the cancer, not the cause.