We regard sialolipoma as a distinct variant of salivary gland lipoma that can occur in both the major and minor salivary glands. Superficial parotidectomy, or surgical resection in the case of palatal tumours, is an appropriate treatment for this benign tumour.

Hybrid carcinomas of the salivary gland are a recently defined and rare tumor entity, consisting of two histologically distinct types of carcinoma within the same topographic area. In this study, we examined nine such cases, which mainly arose in the parotid gland (seven cases), with an additional one each from submandibular and lacrimal glands, and analyzed their clinicopathologic profiles, including immunohistochemical features and p53 gene alterations. The prevalence of hybrid carcinomas was 0.4% among the 1863 cases of parotid gland tumors in our series. The nine patients comprised five men and four women, ranging in age from 40 to 81 years (mean, 62 y). Tumor size ranged from 2 to 10 cm (mean, 4.2 cm). Of the seven patients who were followed up, two were alive with disease and five were alive with no evidence of disease, although the follow-up period was short. Three cases had cervical lymph nodal metastases. The combinations of carcinoma components in our hybrid carcinomas were as follows: epithelial-myoepithelial carcinoma and basal cell adenocarcinoma in two cases, epithelial-myoepithelial carcinoma and squamous cell carcinoma in one case, salivary duct carcinoma and adenoid cystic carcinoma in two cases, myoepithelial carcinoma and salivary duct carcinoma in one, acinic cell carcinoma and salivary duct carcinoma in one, and squamous cell carcinoma and salivary duct carcinoma in two. Although the proportion of each carcinoma component in a tumor mass varied from case to case, the minor component always represented >10% of the area. Differences in cellular composition were studied by immunohistochemistry and electron microscopy. The Ki-67-labeling index apparently differed between the two carcinoma elements in five cases. Diffusely positive p53 immunoreactivity was observed in four cases, restricted to the more aggressive component in each pair. Furthermore, p53 gene alteration analysis of these p53-positive cases revealed that all and three cases demonstrated loss of heterozygosity at p53 microsatellite loci and p53 gene point mutations, respectively, which were detected only in the p53-immunoreactive carcinoma component. Therefore, there is the possibility that such molecular-genetic events take an integral part for inducing the transformation from histologically lower to higher grade tumor during the hybrid carcinoma genesis of the salivary glands.

Pulmonary large-cell neuroendocrine carcinoma (LCNEC) is a newly proposed clinicopathologic entity; a few cases of LCNEC have been reported in other sites, such as the uterine cervix and the thymus. In the salivary glands, LCNEC is extremely rare and is not recognized as a specific entity in the World Health Organization classification. We retrospectively reviewed from our files 1675 cases of surgically resected primary parotid gland tumors and found 2 cases of LCNEC that fulfilled the criteria of pulmonary LCNEC. These cases occurred in 72-and 73-year-old men who had short histories of enlarging parotid gland tumors. The tumors were composed of large cells that exhibited organoid, solid, trabecular, and rosette-like growth patterns with a high mitotic rate and a conspicuous tendency for necrosis. The tumor cells were polygonal and characterized by a moderate nuclear:cytoplasmic ratio, coarse chromatin, and conspicuous nucleoli. Immunohistochemical examination revealed that the tumor cells were positive for six general neuroendocrine markers, cytokeratin, p53, bcl-2, epidermal growth factor receptor, and cyclin D1. Markedly reduced expressions of p21 Waf1 and p27 Kip1 were also noticed. The Ki-67 labeling index was more than 50% in both cases. One case showed loss of heterozygosity at TP53 accompanied by a p53 gene point mutation. Loss of heterozygosity at chromosome 9p21 was detected in both cases; one was accompanied by a p16 gene silent point mutation.Both patients died of the disease, with recurrence 5 months and 4 years after surgery, respectively. These findings indicate that LCNEC is a rare but distinct salivary gland tumor with highly aggressive biologic behavior. Multiple alterations of cell cycle regulators and tumor suppressor genes may play an important role in presenting the biologic characteristics of this rare parotid gland tumor.KEY WORDS: bcl-2, Cyclin D1, K-ras, Large-cell neuroendocrine carcinoma, p16, p27 Kip1

No abstract

Retinoblastomas exhibit a unique form of differentiation to produce cell elements similar to those seen in a photoreceptor cell. An ultrastructural study was performed on 29 cases of retinoblastoma to further clarify the cytologic characteristics of the tumor cells. The age of the retinoblastomas averaged 17.1 months and the tumor cells showing photoreceptor differentiation were demonstrated in 10 cases (35%). The findings were especially notable in retinoblastomas with Flexner-Wintersteiner rosette formation (seven cases, 28%). Similar photoreceptor differentiation was also evident in solid cell clusters without rosette formation (four cases, 14%). The presence of photoreceptor elements was assumed to be significantly frequent both in Flexner-Wintersteiner rosettes and in the solid cell clusters. The cell cytoplasm also showed proliferation of long mitochondria and microtubules, reflecting photoreceptor differentiation. The hereditary-type retinoblastoma showed more advanced cell differentiation than the non-hereditary type. Photoreceptor differentiated retinoblastoma showed rather indolent growth compared with the undifferentiated type, and the former can expect a curative treatment by operation. These observations provide additional findings of the biological nature of retinoblastomas.