RESUMO
<p><b>OBJECTIVE</b>To study the clinicopathological features, immunophenotype, differential diagnosis and prognosis of low-grade nasopharyngeal papillary adenocarcinoma (LGNPPA).</p><p><b>METHODS</b>The histopathological features and clinical and pathological data of nine cases of LGNPPA were retrospectively analyzed. Immunohistochemistry (Two-step EnVision methods) was used to evaluate the expression of CKpan, vimentin, CK7, CK19, TTF-1 and TG; in situ hybridization was used to detect Epstein-Barr virus mRNA (EBER); and flow-through hybridization was used to evaluate the presence of human papilloma virus (HPV).</p><p><b>RESULTS</b>The mean age for the nine patients (eight males, one female) was 45.3 years (range 23 to 62 years). Microscopically the tumors were characterized by lobulated, papillary and glandular structures with patchy distribution of spindle cells. The papillary interstitial tissue was edematous, myxoid or hyalinized. The tumors were unencapsulated and infiltrated into the surrounding stroma. Four cases displayed transition between normal nasopharyngeal epithelium to neoplastic cells; and one case contained psammoma bodies. Five cases were strongly positive for CKpan, vimentin, CK7, CK19, TTF-1, and were focally positive for EMA and CD117. These five cases were all negative for TG, CK5/6, CK20, S-100 protein, p63, Calponin and SMA. In situ hybridization for EBER and flow-through hybridization for HPV were negative in all five cases. Follow-up data showed no post-operative recurrence of the LGNPPA.</p><p><b>CONCLUSIONS</b>LGNPPA is a rare low-grade neoplasm with distinct morphological characteristics. Its diagnosis is primarily based on the site of lesions and the histological features. The diagnosis and differential diagnosis of LGNPPA could be aided by immunohistochemical staining. LGNPPA may originate from nasopharyngeal epithelium; and the prognosis is good with simple and complete resection.</p>