Answer: Well-differentiated sinonasal adenocarcinoma, non-intestinal type

Histology: The lesion exhibits a papillary pattern of growth. The papillary fronds are lined by columnar resorptive-type cells and scattered goblet cells. The nuclei are elongated, cytologically bland and uniformly aligned. Invasive growth and overtly malignant cytologic features are not identified.

Discussion: Several investigators have attempted to further subclassify the sinonasal intestinal-type adenocarcinomas (see discussion to Case 4) based on cytoarchitectural features. Although terminology varies, the papillary type demonstrates a predominant papillary architecture, minimal cytologic atypia, and rare mitotic figures. It is regarded as a well-differentiated form of sinonasal intestinal-type adenocarcinoma. The colonic type grows as infiltrating tubules and glands, and exhibits cellular pleomorphism and increased mitotic activity (see Case 4). This is the type that most closely resembles colonic adenocarcinoma. The colonic type is regarded as a moderately differentiated form of sinonasal intestinal-type adenocarcinoma. The solid type exhibits solid and trabecular growth. The cells show loss of differentiation. This is regarded as a poorly-differentiated form of sinonasal intestinal-type adenocarcinoma. Finally, some sinonasal intestinal-type adenocarcinomas produce mucin. The presence of malignant glands within lakes of mucin has the appearance of a colonic colloid carcinoma. The presence of intracellular mucin gives rise to signet ring cell carcinomas.

The subtyping of sinonasal intestinal-type adenocarcinomas has prognostic significance. The mucinous subtypes (particularly the signet ring-cell carcinomas) and solid subtypes are aggressive tumors associated with a dismal prognosis. The papillary subtype of sinonasal intestinal-type adenocarcinoma is clearly malignant, but it is less aggressive that the other variants. It has a limited capacity to metastasize, and it is associated with a 5 year survival rate of about 80%.