Which statement is true regarding differentiating cholangiocarcinoma from pancreatic adenocarcinoma using immunohistochemistry?

• A. IHC alone can reliably differentiate them.
• B. IHC alone cannot differentiate them.
• C. IHC is not helpful at all for this distinction.
• D. Only imaging can distinguish them.

Answer: (B)

The important idea here is that immunohistochemistry shows what kind of ductal differentiation the tumor has, but it cannot by itself tell you whether a tumor in this region is cholangiocarcinoma or pancreatic adenocarcinoma. These two cancers often share similar IHC profiles—many express CK7 and CK19 and have overlapping mucin patterns—so there isn’t a single marker that definitively distinguishes them. Because of that, IHC results must be interpreted alongside imaging and the tumor’s location (for example, whether the mass clearly arises from the bile ducts or from the pancreas) and the clinical context. IHC still plays a helpful role in supporting a biliary vs pancreatic origin and in ruling out other sites, but it’s not reliable as the sole discriminator.