Sialoblastoma: a clinicopathologic and immunohistochemical study of 7 cases

Sialoblastoma is a rare congenital or perinatal salivary tumor that varies in histologic features and biologic potential. Seven cases from the files of the Armed Forces Institute of Pathology are presented. These tumors occurred in 4 males and 3 females with ages ranging from prenatal to 6 months at the time of discovery. Five lesions originated from the parotid gland; 2 lesions were from the submandibular gland. All lesions presented as nodular to multinodular swellings and ranged in size from 2.0 to 7.0 cm. The principal sign or symptom was rapid growth. Two histologic patterns with differing behavior predominated: (1) a favorable pattern had semiencapsulation of cytologically benign basaloid tumor cells with intervening stroma; and (2) an unfavorable histology of anaplastic basaloid tumor cells, minimal stroma, and broad pushing to infiltrative periphery. Four and three tumors had favorable and unfavorable growth patterns, respectively. One unfavorable lesion had vascular invasion, and another demonstrated perineural invasion. All 3 tumors with unfavorable histology recurred. Tumor cells in 3 cases were immunohistochemically reactive for keratin, S-100, smooth muscle actin, and calponin to varying degrees. All 3 tumors were reactive for p63. α-Fetoprotein was expressed in 2 unfavorable tumors. Ki67 was expressed at 3% in a favorable tumor and 40% and 80% in the 2 unfavorable lesions. Treatment involved surgical excision. One patient received adjuvant chemotherapy. Two sialoblastomas resulted in recurrences within a year and another developed a recurrence after 4 years. One sialoblastoma developed lung metastasis within 1 month of the original biopsy. Although a clinical correlation is suggested by a favorable/unfavorable histologic grading system the biologic behavior is nonetheless considered unpredictable.