Head and Neck Pathol (2009) 3:69–77 Fig. 3 Adenoid cystic carcinoma with high grade transformation. a A conventional cribriform component with monomorphic nuclei on top transitions to a pleomorphic highly atypical adenocarcinoma on bottom. b The transformed component metastasized to a cervical lymph node Table 4 Comparison of solid conventional adenoid cystic carcinoma and high grade transformationa 73 Solid conventional adenoid cystic carcinoma Adenoid cystic carcinoma with high grade transformation Dark, homogeneous Delicate Present but indistinct At most twice the size of grade I-II ACC nuclei. Uniform size distribution Scant to nearly absent Solid nests, rarely spanning more than a 403 high power ﬁeld Paucicellular myxoid or hyaline Focally present, usually punctuate Rarely present Generally \10/hpf Present and complete \50% Rare Vesicular or heterogeneously dispersed Thickened or irregular Prominent central At least 2–3 times the size of grade I-II ACC nuclei (typically more). At least 2 fold nuclear variation Scant to moderate Solid conﬂuent nests to sheets often ﬁlling a 403 high power ﬁeld Fibrocellular desmoplastic Often present, punctuate to large zones Often present Micropapillae, squamoid areas Usually [10/hpf Incomplete and at least focally absent [50% Common Features Chromatin Nuclear membranes Nucleoli Nuclear size Cytoplasm Growth Stroma Comedonecrosis Microcalciﬁcations Unique features Mitoses Abluminal cell layer presence by immunohistochemistry Ki-67 p53 overexpression (strong reactivity in >50% of cells) Bold = Major Features a Adapted from Seethala et al. [15] These tumors have an exceptionally poor prognosis with a median survival ranging from 12 to 36 months, and may thus be even more aggressive that solid or ‘grade 3’ ade- noid cystic carcinoma. Unlike conventional adenoid cystic carcinoma, this tumor has a lymph node metastatic rate of over 50% (Fig. 3b). Thus if a transformed component is found in an adenoid cystic carcinoma, a neck dissection is likely warranted. Summary recommendations for grading of adenoid cystic carcinoma: • Report predominant growth pattern (tubular, cribriform, or solid) • If any solid component is present give rough estimate of percentage