Selective Immunohistochemical Comparison of Polymorphous Low-Grade Adenocarcinoma and Adenoid Cystic Carcinoma
Purpose
Polymorphous low-grade adenocarcinoma (PLGA) is a salivary gland malignancy characterized by indolent growth and a low rate of metastasis. PLGA shares histological features with adenoid cystic carcinoma (ACC), including infiltrating solid and cribriform patterns, presence of cystic spaces, and neurotropism. The degree of polymorphism of PLGA presents diagnostic challenges, particularly in small biopsy specimens. Immunohistochemical reactions to differentiate PLGA from the more aggressive ACC would be extremely valuable but controversy exists in the current literature regarding their utility. This study examines the potential use of c-kit, Ki-67, smooth muscle actin (SMA), and muscle-specific actin (MSA) as ancillary markers for distinguishing PLGA from ACC.
Patients and Methods
Medical records of 20 cases of PLGA treated at the Massachusetts General Hospital were reviewed. Patient demographic data and tumor-specific information were elicited. Formalin-fixed paraffin-embedded sections from 10 of these cases and 12 comparison cases of ACC were accessed. The histologic diagnoses were confirmed and immunohistochemical staining using antibodies to c-kit, Ki-67, SMA, and MSA was employed to determine differences in staining.
Results
PLGA showed a significantly weaker immunohistochemical expression of c-kit compared with ACC (P = < .001). Ki-67, correlating with proliferative behavior, was more weakly expressed in PLGA (P = .091). The exuberant myoepithelial component of ACC resulted in stronger staining with SMA and MSA (P = .047; P = .065, respectively).
Conclusions
Statistically significant immunohistochemical staining patterns using c-kit and SMA in this study support their potential use as markers to differentiate PLGA from ACC in cases where the diagnosis can be challenging.
⁎Resident, Department of Oral and Maxillofacial Surgery, Massachusetts General Hospital, Harvard School of Dental Medicine, Boston, MA
†Assistant Professor, Department of Pathology, Massachusetts General Hospital, Harvard Medical School, Boston, MA
‡Professor, Department of Oral and Maxillofacial Pathology, Boston University Goldman School of Dental Medicine, Boston, MA
§Associate Professor, Department of Oral and Maxillofacial Surgery, Massachusetts General Hospital, Harvard School of Dental Medicine, Boston, MA
Address correspondence and reprint requests to Dr August: Massachusetts General Hospital, Department of Oral and Maxillofacial Surgery, 55 Fruit Street, Warren 1201, Boston, MA 02114
ABSTRACT