Adenosquamous carcinoma of the pancreas

Adenosquamous carcinoma of the pancreas is a rare, highly aggressive malignancy, clinically indistinguishable from the more common pancreatic ductal adenocarcinoma. Their defining pathological and imaging characteristics are the frequent presence of central necrosis and vascular invasion.

Terminology

These tumors have been variably referred to as adenoacanthomas, mixed squamous and adenocarcinomas and mucoepidermoid carcinomas ¹⁰.

Epidemiology

Adenosquamous carcinoma makes up ~5% (range 1-10%) of all exocrine pancreatic malignancies ^8,9.

These tumors occur in older adults (mean age of 68 years) ⁹, with a slight male predilection (M:F = 1.5:1) ⁷.

Clinical presentation

Adenosquamous carcinoma exhibits the same clinical characteristics as the more common pancreatic ductal adenocarcinoma and distinguishing between the two based on clinical findings alone is not possible ⁸.

Most patients are asymptomatic until advanced disease develops, with the main clinical findings being weight loss, jaundice and non-specific abdominal pain ⁷.

CA19-9 is the most commonly elevated tumor marker ⁶.

Pathology

The diagnosis of an adenosquamous carcinoma requires at least 30% squamous histology present in the tumor ¹⁰.

Tumors exhibiting a lower proportion of squamous cells are termed “pancreatic cancer with squamous differentiation” ⁷.

Radiographic features

CT

Adenosquamous carcinomas typically appear as ill-defined, lobulated lesions ^4-6,9,  hypoattenuating or isoattenuating on non-enhanced CT ^4,6.

On contrast-enhanced CT the majority of these tumors exhibit a central hypodense, non-attenuating area of variable size corresponding to necrosis, a characteristic that differentiates them from pancreatic ductal adenocarcinomas ^2,3,5,9.

A defining feature of adenosquamous carcinoma is progressive ring enhancement ^6,9. Invasion of the adjacent vessels and tissues is frequent ^2,4-6. Dilatation of the main pancreatic duct upstream to the lesion can be seen in about 50% of adenosquamous carcinomas ^4-6. Calcification and hemorrhage are not typical features of these tumors ^2-4,6.

MRI

The solid component of the tumor exhibits a decreased signal compared to normal parenchyma on T1WI and increased signal on T2WI ^4-6. DWI shows a slight hyperintensity, with hypointensity on ADC images ⁶.

Ring enhancement can usually be better appreciated on MRI ⁶.

Treatment and prognosis

Due to the relative rarity of these tumors there are no established treatment protocols ⁸. The only available treatment is resection, with a median survival of 12 months ¹.

History and etymology

The earliest description of this tumor was by the German pathologist, Gotthold Herxheimer (1872-1936), in 1907 who called it a "cancroide" ¹⁰.

Differential diagnosis

• pancreatic ductal adenocarcinoma

  • necrosis less common (40% vs 100%)

  • tumor thrombi are rare (6% vs 37.5%) ⁵

  • adenosquamous carcinoma is more often located in the pancreatic tail ⁹

• acinar cell carcinoma

  • calcification present in 50%

• pancreatic neuroendocrine tumor (pNET)

  • typically hypervascular

  • may exhibit calcification

• solid pseudopapillary tumor

  • usually well encapsulated

  • may show calcification

  • typically in young women