PAS & PAS-D always a mystery until now? PAS is a special stain not an immunostain. PAS stain without treatment with diastase or diastase sensitive stains glycogen, neutral mucins, glycoproteins, fungi and sulphate mucins (pulmonary alveolar proteinosis). On the other hand acinar cell carcinoma of pancreas, cowper glands of prostate, alveolar soft part sarcoma and some mucins stain after treatment with diastase.