Per Å. Jakobsson

Mucoepidermoid carcinoma of the parotid gland

In a histologic re‐examination and reclassification of a series of 1678 tumors of the parotid gland, 63 (3.7%) exhibited the structures characteristic of mucoepidermoid carcinoma. A long‐term follow‐up study showed that mucoepidermoid carcinoma differs from acinic cell and adenoid cystic carcinoma in that the determinate survival rate does not fall markedly when the follow‐up exceeds 5 years. This implies that the prognosis based on the determinate survival rate can be evaluated after a 5‐year follow‐up study. Histologically, the 63 tumors have been divided into two subgroups, one consisting of 20 tumors exhibiting invasive growth (high grade malignant) and the other of 43 without invasive growth (low grade malignant). The follow‐up study showed the difference between the prognosis in the two groups. In order to improve the poor prognosis in high grade malignant mucoepidermoid carcinoma, the authors recommend that parotidectomy should be routinely combined with radical neck dissection in high grade malignant tumors.

Oncocytoma of the parotid gland: Neoplasm or nodular hyperplasia?

In a histologic re‐examination and re‐classification of parotid tumors in 1,678 patients treated by surgery, 13 cases of oncocytoma were found. Five patients had bilateral tumors. The cell picture in oncocytoma is very characteristic, made up of oncocyte‐like cells with eosinophilically granulated abundant cytoplasm, and often also of clear cells. Metastases or death in oncocytoma did not occur in any case, but local “recurrence” was seen in 4 of the 13 cases. Oncocytoma often shows multinodular growth, and oncocytic foci are very often found in the surrounding glandular tissue. Of the 5 patients who had bilateral tumors, 2 had synchronous tumors. The high frequency of multinodular and bilateral growth observed in the present series supports earlier theories that oncocytoma is not a real neoplasm but a nodular hyperplasia. The main differential diagnoses are benign mixed tumor with oncocytic foci and acinic cell carcinoma.

Mucus-producing adenopapillary (non-epidermoid) carcinoma of the parotid gland

In a histologic reexamination and reclassification of a series of 1,678 tumors of the parotid gland, 47 (2.8%) exhibited structures characteristic of mucusproducing adenopapillary (non‐epidermoid) carcinoma. There seems to be a rather close relationship between this tumor type and mucoepidermoid carcinoma. The differential diagnostic difficulties between these two groups can perhaps explain why in earlier works the groups of mucus‐producing adenopapillary carcinoma are so small and mostly contain only occasional cases. Our strict criterion of mucoepidermoid carcinoma, demanding the demonstration of squamous differentiation, separates these tumors from mucus‐producing adenopapillary (non‐epidermoid) carcinomas. This can explain why the group of mucoepidermoid carcinomas comprised 3.7% in our series as compared to 4–12% in other works. Histologically, we have divided the 47 tumors into two subgroups: one consisting of 28 invasive growing tumors (high‐grade malignant) and one of 19 non‐invasive growing tumors (low‐grade malignant). The high‐grade malignancies have a poor prognosis with a determinate survival rate similar to adenoid cystic carcinoma, and the prognosis of the low‐grade type is comparable to that of low‐grade mucoepidermoid carcinoma. In order to improve the poor prognosis in the high‐grade mucus‐producing adenopapillary carcinoma, the authors recommend that parotidectomy should be routinely combined with radical neck dissection.