Introduction

The classification of salivary gland tumours includes a large number of lesions, some of which exhibit a wide range of histopathologic variants. Recently, Seifert et al. [10] described five cases of "very rare tumoural entities, each of which conforms with an exactly defined tumour category" and designated them as hybrid tumours. To date, less than twenty cases have been published in the English literature [1, 3, 4, 6, 7, 10, 12, 14, 15].

The purpose of this article is to present two new cases of hybrid tumours of the salivary glands, focusing on their histomorphological features, as well as comparing them with previously reported cases of these unusual lesions.

Case report

Case 1

A 49-year-old woman complained of a painless palatine tumour that had been growing slowly for 10 years, but in the last 8 months, it had grown more quickly and become ulcerated. On clinical examination an exophytic, multilobulated and ulcerated mass involving both the right hard and soft palate was evident. The lesion measured 3.5 cm and extended beyond the midline. A neck examination disclosed no lymphadenopathy. Treatment consisted of maxillectomy and postoperative radiotherapy (60 Gy). Thirteen months later the patient is alive with no evidence of recurrence.

Gross examination disclosed a 3.5×3.5×2.5 cm ulcerated exophytic neoplastic growth located along the hard palate, which extended back to the soft palate and infiltrated beyond the midline. Macroscopically, the tumour was yellowish white, firm and partially solid, with small cystic spaces scattered in the lesional tissue.

Microscopic examination disclosed two morphological patterns: adenoid cystic carcinoma and mucoepidermoid carcinoma. The first was composed of a predominantly solid pattern with occasional areas of cribriform morphology. The mucoepidermoid component showed a cystic pattern with abundant mucous-producing cells and a moderate amount of intermediate and epidermoid cells (Fig. 1a and Fig. 1b).

Fig. 1.
figure 1

a Case one shows a mucoepidermoid carcinoma component (HE, ×250). b Case one shows an area of adenoid cystic carcinoma with a cribriform pattern (HE, ×250)

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Case 2

The patient was a 71-year-old man who presented with a 7-month history of a tumour mass located in the right hard and soft palate. The lesion was firm and tender. The patient also had associated facial paralysis. A CT scan disclosed a tumoural mass located within the right nasal fossa and maxillary sinus, which produced deviation of the nasal septum and thickening of the anterior ethmoidal cells. Treatment consisted in a right maxillectomy and postoperative radiotherapy of 60 Gy. After 36 months of follow-up, there has been no evidence of recurrent disease.

Macroscopically, the surgical specimen showed a tumour located in the hard and soft palate that infiltrated the maxillary sinus. The tumour was solid, yellowish and firm in consistency with some cystic areas.

Microscopic examination disclosed two different morphological patterns: adenoid cystic carcinoma and epithelial-myoepithelial carcinoma. The first one exhibited tubular and cribriform patterns, while the epithelial-myoepithelial carcinoma showed the classic pattern, with ductal cells surrounded by myoepithelial cells (Fig. 2a and Fig. 2b).

Fig. 2.
figure 2

a Case two shows adenoid cystic carcinoma with a cribriform component (HE, ×150). b Case two with epithelial-myoepithelial carcinoma showing ductal central differentiation surrounded by clear cells (HE, ×250)

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Discussion

Hybrid tumours are very rare salivary gland neoplasms composed of two or more different tumoural entities in a single neoplasm that arise within a definite topographical region [10]. It is important to differentiate these neoplasms from collision tumours, which are lesions that originate in different regions but coalesce in a particular area [3]. Also, these lesions should be distinguished from tumours with biphasic differentiation, which are single entities composed of two different cellular types, such as epithelial-myoepithelial carcinomas and pleomorphic adenomas, for example [6, 7, 12].

It is interesting to note that most of the previously published cases of hybrid tumours of the salivary glands have shown a higher incidence of adenoid cystic carcinoma, which is also evident in the present series. The first case described in this article presents a mixture of adenoid cystic carcinoma plus mucoepidermoid carcinoma, and the tumour in the second was composed of adenoid cystic carcinoma and epithelial-myoepithelial carcinoma. These findings suggest that the frequent occurrence of hybrid tumours associated with this particular type of adenocarcinoma could be higher than has been estimated (Table 1).

Table 1. Hybrid tumours of salivary glands. NED no evidence of disease, AWOD alive without disease, AWD alive with disease
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In those cases where both cellular components are found in biphasic neoplasms, their origin may be explained by a single precursor cell that gives rise to both entities; however, most of the reported hybrid tumours have been composed of one biphasic entity and one that is not, which suggests that these neoplasms may be derived from salivary duct stem cells [2, 8, 9, 13].

Shikani et al. in 1993 reported two cases of Warthin's tumours associated with other neoplasms and presented a review of the literature, where they found 42 similar cases [11]. According to the histopathologic features described in their cases and the criteria stated by Seifert and Donath to diagnose a hybrid tumour, some of them could be classified as this entity [10].

The relevance of diagnosing hybrid tumours lies in the fact that the component with the higher grade of malignancy determines the biological behaviour of the neoplasm and, consequently, determines the proper management of each case.