Table 1.

Overview of undifferentiated carcinoma

Epidemiology
	• The frequency in malignant neoplasms of the pancreas is 0.3–7%
	• The median age at diagnosis is around the 60s.
	• There is a slight male predominance.
Clinical features
	• Tend to show larger size (the median size was reported to be 60–90 mm).
	• Slightly more frequently seen in the pancreatic body/tail.
	• No specific symptoms are seen.
Diagnosis
	• Both CEA and CA19-9 are mostly not elevated.
	• CT shows similar imaging features to pancreatic cancer.
	• EUS-TA is essential for the diagnosis, especially in the advanced stage.
Prognosis
	• UC patients have significantly shorter survival compared with PC patients.
	• UCOGCs have been reported to have relatively long survival compared with UC.
Pathological findings
	Anaplastic UCs • Pleomorphic mononuclear cells admixed with bizarre-appearing giant cells with eosinophilic cytoplasm are present. Neoplastic cells are non-cohesive and lack gland formation.
	Sarcomatoid UCs • Spindle-shaped cells mimicking sarcomas are present.
	Rhabdoid UCs • A rare subtype of sarcomatoid UCs. Neoplastic cells have rhabdoid inclusions.
	Carcinosarcomas • Admixture of both roundish epithelioid cells and spindle sarcomatous cells.
	UCOGCs • Admixture of neoplastic pleomorphic mononuclear cells and multinucleated OGCs. OGCs are positive for leucocyte markers and considered non-neoplastic.
Molecular features
	• Similar to pancreatic cancer, KRAS, TP53, CDKN2A/B and SMAD4 are commonly observed.
	Anaplastic UCs • EMT-related proteins are highly expressed.
	Sarcomatoid UCs • PD-L1 is highly expressed.
	Rhabdoid UCs • Genomic alterations in SWI/SNF complex subunits are frequently observed.
	Carcinosarcomas • Both carcinomatous and sarcomatous components share identical alterations of KRAS and TP53.
	UCOGCs • PD-L1 is highly expressed.
Treatment
	• Basically, only surgical resection can offer curative treatment for patients with UC.
	• To date, no clear evidence exists for chemotherapy for UC.
	Anaplastic UCs • A retrospective cohort study and case reports indicate that a paclitaxel-containing regimen is a reasonable option for the treatment of patients with unresectable UC.
	UCOGCs • Promising responses to ICIs for UCOGCs have been described in case reports.

CT, computed tomography; EUS-TA, endoscopic ultrasound-guided tissue acquisition; UC, undifferentiated carcinoma; OGCs, osteoclast-like giant cells; UCOGCs, UC with OGCs; EMT, epithelial–mesenchymal transition; PD-L1, programmed death-ligand 1; SWI/SNF, SWItch/Sucrose Non-Fermentable; ICIs, immune checkpoint inhibitors.