A 55 year old man presents to a physician with jaundice. Ultrasonography demonstrates a 5 cm mass in the head of the pancreas. Endoscopic retrograde cholangiopancreatography with cytologic sampling demonstrates cells with large hyperchromatic nuclei and a high nuclear/cytoplasmic ratio. A few small glands composed of these cells are also seen in the cytologic preparation. The overall prognosis for this man will be most similar to that of a patient with which of the following malignancies?