Sialoblastoma of the submandibular gland: a distinct entity?

Fine-Needle Aspiration of Parotid Gland Sialoblastoma. Two New Cases and Literature Review

Sialoblastoma is an exceedingly rare, low-grade malignancy, most frequently arising in the parotid gland. Only four case reports detailing the cytomorphology of this neoplasm exist in the English literature. Here, we describe the cytological features, histopathology, and clinical data of sialoblastomas presented at birth in two additional patients. Both neoplasms were initially examined by fine-needle aspiration (FNA) followed by surgical excision of the tumors. Smears showed hypercellularity and basaloid round to oval cells isolated or arranged in three-dimensional clusters. Papillary and acinar configurations, metachromatic pink stromal fragments, and hyaline globules were also present. One case was diagnosed as a neoplasm of unclear malignant potential and the second as malignant.

Sialoblastomas With Solid Pattern Have FGFR2 Mutations and an Unfavorable Prognosis

Although sialoblastoma (SBL) is defined as a low-grade malignant salivary gland anlage neoplasm in the 2022 World Health Organization (WHO) Classification of Head and Neck Tumors, its histology, genetics, and behavior remain controversial due to the rarity of the tumor. Here, we performed the first comprehensive clinical, histologic, and molecular analyses of 8 SBLs to better understand their pathogenesis and prognosis. This cohort consisted of 5 boys and 3 girls, with ages ranging from birth to 9 years at diagnosis. Tumors occurred in the parotid (4), cheek (3), and submandibular glands (1). Histologically, 5 tumors primarily presented as a solid pattern consisting of primitive basaloid epithelial cells, often with necrosis. Three tumors exhibited a non-solid pattern, with 1 tumor mainly showing epithelial-myoepithelial carcinoma (EMC)-like histology, whereas the other 2 tumors exhibited basal cell adenoma (BCA)-like histology. All 5 solid SBLs harbored FGFR2 mutations, and 1 also harbored mutations in PALB2, AR, and MAP2K1. In contrast, non-solid pattern tumors were characterized by HRAS mutations or significant β-catenin nuclear positivity. All 5 solid tumors recurred, 3 of them developed distant metastases, and 2 died 40 and 44 months after diagnosis. Three non-solid tumors showed no evidence of disease recurrence at 49, 144, and 132 months, suggesting a relatively favorable prognosis. Overall, SBLs can be stratified into solid and non-solid patterns, with solid pattern tumors usually having FGFR2 mutations, increasing the risk of recurrence and metastasis. This stratification underscores the importance of genetic and morphologic profiling for predicting the prognosis of SBLs.

The Cellular and Molecular Landscape of Synchronous Pediatric Sialoblastoma and Hepatoblastoma

Sialoblastoma (SBL) is an infrequent embryonal malignant tumor originating from the salivary gland, resembling primitive salivary gland anlage, whereas hepatoblastoma (HB) is the most common pediatric liver malignancy. The simultaneous occurrence of both tumors is extremely rare. Here we reported a case of a 6-month-old infant diagnosed with synchronous SBL and HB. The patient received neoadjuvant chemotherapy followed by surgical resection. Fresh tissues of both tumors were collected before and after chemotherapy, which were further profiled by whole exome sequencing (WES) and single-cell RNA sequencing (scRNA-seq). WES analysis revealed potential somatic driver mutation PIK3CA p.Glu454Lys for SBL and canonical mutation CTNNB1 p.Ser45Pro for HB. No shared somatic variants or common copy number alterations were found between SBL and HB primary tumor samples. Though scRNA-seq, single-cell atlases were constructed for both tumors. SBL may recapitulate a pre-acinar stage in the development of salivary gland, including basaloid, duct-like, myoepithelial-like, and cycling phenotypes. In the meantime, HB was composed of tumor cells resembling different stages of the liver, including hepatocyte-like, hepatic progenitor-like, and hepatoblast-like cells. After chemotherapy, both tumors were induced into a more mature phenotype. In terms of transcriptional signatures, SBL and HB showed enhanced expression of epithelial markers KRT8, KRT18, and essential embryo development genes SDC1, MDK, indicating the disruption of normal embryo epithelium development. Finally, heterozygous deleterious germline mutation BLM and FANCI were identified which could predispose the patient to higher cancer risk. It partially explained the reason for the co-occurrence of SBL and HB. Taken together, we provided valuable resources for deciphering cellular heterogeneity and adaptive change of tumor cells after chemotherapy for synchronous SBL and HB, providing insights into the mechanisms leading to synchronous pediatric tumors.