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Sialoblastoma in adults: distinction from adenoid cystic carcinoma
Irving Dardick1, Thomas D Daley, R John McComb
1Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, Toronto, Canada. idardick@pathologyimagesinc.com
Insights
Sialoblastoma, a rare infant cancer, can occur in adults and shares features with adenoid cystic carcinoma. This study suggests sialoblastoma has a better prognosis than adenoid cystic carcinoma.
Area of Science:
- Oncology
- Pathology
- Pediatric Oncology
Background:
- Sialoblastoma is primarily a disease of infancy, with limited reported cases in adults.
- A cribriform growth pattern is observed in approximately one-third of pediatric sialoblastoma cases.
- Adult cases with similar histological features have historically been misdiagnosed as adenoid cystic carcinoma.
Observation:
- This report details three adult cases exhibiting primitive histopathology characteristic of sialoblastoma.
- Key features include basaloid tumor cells, bilayered ductal structures, and a fibromyxoid stroma.
- These adult tumors resemble fetal salivary gland or salivary gland with arrested development.
Findings:
- Sialoblastoma, irrespective of age or growth pattern (cribriform or not), demonstrates a more favorable prognosis compared to adenoid cystic carcinoma.
- Histological analysis revealed distinct features differentiating sialoblastoma from adenoid cystic carcinoma, even in adult presentations.
- Long-term follow-up, including a 28-year case, supports the favorable prognosis of sialoblastoma.
Implications:
- This study expands the understanding of sialoblastoma by including adult cases, challenging previous diagnostic assumptions.
- Accurate diagnosis of sialoblastoma in adults is crucial for appropriate treatment and prognosis assessment.
- Recognizing sialoblastoma's distinct histological features and favorable prognosis can improve patient outcomes and guide therapeutic strategies.
Abstract:
Essentially, sialoblastoma is a disease of infancy with the oldest case presenting at 4 years of age. About one third of pediatric sialoblastoma cases will have a cribriform growth pattern. No adult cases have been reported with a specific diagnosis of sialoblastoma. If even focal cribriforming were present, such cases have undoubtedly been diagnosed as adenoid cystic carcinoma. Such was the circumstance in the 3 adult tumors presented in this report. Each case, however, has the primitive histopathology with discrete nests of basaloid tumor cells, associated bilayered ductal structures and the fibromyxoid stroma characteristic for sialoblastoma with its resemblance to fetal salivary gland or salivary gland with arrested development. One key example has 28-year follow-up. Sialoblastoma, whether in a child or adult with or without a cribriform growth pattern, appears to have a more favorable prognosis than adenoid cystic carcinoma. Aspects of the histological differential diagnosis of these 2 tumors are discussed.
