Dedifferentiated Adenoid Cystic CA
Rare cases of adenoid cystic carcinoma (ACC) undergo dedifferentiation and purse a rapidly aggressive fatal course. They are often associated with TP53 mutations. Dedifferentiated ACC is predominantly composed of poorly-differentiated epithelial component (in contrast to myoepithelial cells) arranged in solid sheets. There is considerable nuclear pleomorphism and increased mitotic activity (including atypical mitoses) and necrosis is frequently present. This image shows conventional ACC with mainly tubular architecture on the right and solid areas of de-differentiated ACC on the left. p53 was negative (by immunohistochemistry) and Ki67 index was 50% in this case.