Spectrum of malignancy in mixed tumors of salivary gland: a morphological and immunohistochemical review of 23 cases.

Malignancy arising in mixed tumors of the salivary gland is a distinct entity that can occur sporadically or in association with a background of pleomorphic adenoma. Carcinoma arising with a background of pleomorphic adenoma is well documented. However, there are rare occurrences of aggressive de novo carcinosarcomas of the parotid that have been reported. Various cell lineages such as the epithelial glandular cells and the stromal spindle cells are involved. We report 23 cases of tumors of the salivary gland comprising 18 cases of carcinoma ex pleomorphic adenoma, four cases of carcinosarcoma of the parotid and one case of benign metastasizing pleomorphic adenoma. The occurrence of various malignancies suggests that this phenomenon is not very uncommon and should be looked for when reporting a mixed tumor.

Cutaneous mixed tumor with lipomatous stroma.

AIM: Mixed tumors are usually composed of two components, one epithelial and the other mesenchymal. The latter component is commonly myxoid or myxochondroid; a massively lipomatous stroma is very unusual. To date, only two cases of mixed tumor of the skin have been reported with this type of stroma. METHODS AND RESULTS: We report the case of a 61-year-old man with a mixed tumor situated on the hand, an unusual site for these tumors, with over 90% of the tumor composed of adipose tissue. The tumor was a well-circumscribed, 4.5-cm mass, with the gross appearance of a lipoma. The lipomatous stroma contained nests and ribbons of epithelial cells, with occasional tubular structures, surrounded by a scarce amount of fibromyxoid tissue. Immunohistochemical study showed findings similar to those seen in classic mixed tumors. CONCLUSION: Together with a few other cases in the skin and parotid gland, this report shows how massive adipose differentiation can arise in a mixed tumor of the skin.

[Perineuriomas and other tumors with perineurial differentiation].

This is a review of the literature on the peripheral nerve sheath tumors with perineural differentiation. The authors provide an overview of the clinicopathological, immunohistochemical, ultrastructural, and genetic features of these neoplasms. Emphasis is laid on various morphological variants of perineurioma (intraneural, retifrm, sclerosing, plexiform, atypical, malignant, etc.) and so-called hybrid tumors (schwannoma-perineurioma, neurofibroma-perineurioma).

Can experimental models of rodent implantation glioma be improved? A study of pure and mixed glioma cell line tumours.

To evaluate the hypothesis that co-implantation of different rodent glioma cell lines might result in experimental brain tumours that more closely resemble human gliomas the neuropathology and immunocytochemical features of implantation gliomas derived from single cell lines (C6, A15A5, F98), two cell lines admixed 50:50 prior to implantation (C6 + F98 and C6 + A15A5) and three cell lines equally admixed (C6 + A15A5 + F98) was studied in the adult Wistar rat. Tumours grew consistently following implantation of the single and the two admixed cell lines, however tumour growth following triple mix implantation was considerably and consistently impaired. The tumours derived from admixed cell lines showed regional heterogeneity with areas characteristic of both the primary cell lines. Foci of lymphocytic infiltrates, tumoural necrosis, often with pseudopallisading, and peritumoural edema were consistent features of all tumours. Limited parenchymal and more extensive perivascular tumoural invasion was seen predominantly in tumours containing the C6 cell line. There were no significant differences in GFAP, vimentin and HSP70 staining between the mixed tumours, although the pure F98 and A15A5 tumours were, unlike the pure C6 gliomas, S-100 negative. Using PCNA expression as a measure of the tumour proliferation all except the tumours derived from the three cell lines mix, which had a staining index of 7-10%, had focal staining indices in viable tumour of between 40-80%. There was focal positive staining in both perilesional brain and in regions of all tumours for the macrophage markers ED-1 and ED-2. None of the three cell lines stained in vitro for either ED1 and ED2 but all were constitutively positive in vitro for OX-6, a proposed marker for antigen presenting cells. The macrophage and lymphocytic response suggest a vigorous but largely ineffective immunological response had been mounted against all tumours. The consistent failure of the triple mix tumours to grow is unexplained. This work has shown the feasibility of producing 'mixed' cell line experimental gliomas by combining two cell lines at the time of innoculation. However, the relative failure to produce (i) mixed tumours that have properties not inherent to either parent cell line and (ii) implantation glioma with three cell lines suggest there are limits to this approach. Admixture of cell lines at the time of implantation therefore does not make experimental glioma models that more closely resemble natural gliomas, and also has some particular disadvantages. This experimental approach is therefore not recommended for use in the study of tumour biology and in evaluating the effectiveness of novel therapies.