Table 1

Histological changes following preoperative (neoadjuvant) chemoradiation in pancreatic ductal adenocarcinoma

	Common histological features	Uncommon histological features
Tumour	Cytoplasmic eosinophilia ▸ Hyperchromasia ▸ Pyknosis ▸ Bizarre nuclei	Oncocytic/‘oncocyte-like’ change ▸ Polygonal cells ▸ Eosinophilic, granular cytoplasm ▸ Round hyperchromatic nuclei ▸ Cherry red, prominent nuclei
	Clear cell change ▸ Wrinkled nuclei ▸ Voluminous clear cytoplasm ▸ ‘Lipoblast-like’ cells ▸ ‘Signet ring-like’ cells	Rhabdoid change ▸ Globular, hyaline intracytoplasmic inclusion ▸ Highlighted by cytokeratin staining ▸ Also known as ‘cytokeratin aggresomes’
	Tumours accompanied by ▸ Mucin pools ▸ Foamy macrophages ▸ Foreign body-type giant cells	Squamous metaplasia/differentiation
	Tumour dissociated into single cells and small islands by streams of fibrosis	Biphasic appearance (seen in one case only) ▸ Oncocytic ductal component ▸ ‘Endocrine’ component (microglandular and organoid patterns) ▸ Negative for neuroendocrine/hormonal markers
	Necrosis ▸ Coagulative (ischaemic) type ▸ Tumour necrosis	Tumour mimicking islet cells ▸ ‘Single-filing’ pattern ▸ Recapitulating islet cell aggregates
	Peritumoural inflammation ▸ Lymphocytes ▸ Plasma cells ▸ Neutrophilc	Erythrophagocytosis ▸ Whole red blood cells ▸ Fragmented (effete) red blood cells
		Intracytoplasmic sharply circumscribed lipid droplet
		Tumour colonising islet cell aggregates ▸ ‘Cookie-cutter’ appearance ▸ ‘Jigsaw-puzzle’ like appearance
Stroma and vessels	Stromal fibrosis ▸ Fibromyxoid stroma with ‘shredded carrot’ appearance ▸ Dense ‘keloidal’ stroma ▸ Cellular ‘nodular fasciitis-like’ stroma	▸ Keloidal fibrosis resembling ‘amyloid’ ▸ Congo red negative
Stroma and vessels	Intimal proliferation of medium-sized vessels
Non-neoplastic pancreas	Pancreatic islet cells ▸ Islet cell hyperplasia ▸ ‘Single-file’ configuration	Marked islet cell hyperplasia mimicking endocrine ‘microadenoma’
	Distorted benign ducts, simulating invasive tumour	Perineural localisation of islet cells imitating perineural invasion
	Hypertrophic nerves	Benign ducts with cytoplasmic eosinophilia
		Benign ducts with squamous metaplasia