Clinical studies on malignant salivary gland tumors encounter multiple difficulties that are derived from a variety of factors: low incidence, various degrees of malignancy according to the different histological types, varied clinical behavior and different anatomical sites.

In this work a retrospective study is carried out of 75 patients with primary malignant salivary gland tumors that were treated over a 23 year period, and the different prognostic factors that could have influenced survival have been evaluated.

I would like to congratulate the authors on the work carried out, for its importance, purpose, meticulousness and the excellent statistical analysis of the results.

The long period of time the study covers adds problems, as in this interval changes have occurred in diagnostic and therapeutic techniques. The widespread use of magnetic resonance as an imaging test; modifications in anatomopathologic studies, together with new histological prognostic factors and immunohistochemical analysis; improvements in complementary treatment with radiotherapy; modifications in the TNM classification of the AJCC, which implies changes in staging for these tumors.

The results presented agree with those obtained by other authors.^1,2 The only differences observed are in the frequency of the histological variants. While in this work cystic adenoid carcinoma, adenocarcinoma and mucoepidermoid carcinoma (in this order) are the most common, in most of the series published it is mucoepidermoid carcinoma and acinic cell carcinoma that are the most common.

In addition to the clinical aspects, molecular and genetic aspects are becoming increasingly more relevant as prognostic factors.³ Immunohistochemical studies for detecting the expression of cell cycle-regulated proteins have shown that pRb2/p130 has a statistically significant influence in the presence of metastasis and in the pathogenesis and progression of some salivary glands neoplasms.⁴ The vascular endothelial growth factor shows an association with the expression of p53 and it has prognostic value in salivary gland carcinoma.⁵ The role of radiotherapy for improving local and regional control is confirmed by Terhaard in an important study⁶ in 538 patients.

Although it may appear surprising, knowing the real incidence of cancer in Spain is difficult. To date in some hospitals there is still no tumor register. The GLOBOCAN data base of the IARC (International Association of Cancer Registries) (available at www-dep.iarc.fr/globocan) makes an estimate as to the incidence of head and neck cancer in our country placing it at 11.513 cases for the year 2002. If we consider that salivary gland tumors represent 3%, the annual incidence of these neoplasms would be 345 cases (this would be an indirect and approximate calculation, as there is no direct estimate of salivary glands).

In spite of the low incidence in our area, the treatment of these neoplasms is very diversified as it is carried out by numerous surgeons with different specializations (preferably but not exclusively maxillofacial). There are very few surgical services that can therefore present a considerable casuistry. This same problem occurs with pathological anatomy services, and not many pathologists can demonstrate considerable experience in these tumors that are so heterogeneous from the histological point of view. The reasons that have been given would justify the importance of multicentric studies, covering epidemiology as well as treatment and results.

Luis Antonio Sánchez Cuéllar
Servicio de Cirugía Oral y Maxilofacial
Hospital Universitario Río Hortega. Valladolid. España

1. Bell RB, Dierks EJ, Homer L, Potter BE. Management and outcome of patients with malignant salivary gland tumors. J Oral Maxillofac Surg 2005;63:917-28.

2. Terhaard CH, Lubsen H, Van der Tweel I, Hilgers FJ, Eijkenboom WM, Marres HA, Tjho-Heslinga RE, de Jong JM, Roodenburg JL. Salivary gland carcinoma: independent prognostic factors for locoregional control, distant metastases, and overall survival: results of the Dutch head and neck oncology cooperative group. Head Neck 2004;26:681-92.

3. Jaehne M, Roeser K, Jaekel T, Schepers JD, Albert N, Loning T. Clinical and inmunohistologic typing of salivary duct carcinoma: a report of 50 cases. Cancer 2005;103:2526-33.

4. Russo G, Zamparelli A, Howard CM, Minimo C, Bellan C, Carillo G, Califano L, Leoncini L, Giordano A, Claudio PP. Expresión of cell cycle-regulated proteins pRB2/p130, p107, E2F4, p27 and pCNA in salivary gland tumors: prognostic and diagnostic implications. Clin Cancer Res 2005;11:3265-73.

5. Lim JJ, Kang S, Lee MR, Pai HK, Yoon HJ, Lee JI, Hon SP, Lim CY. Expression of vascular endothelial growth factor in salivary gland carcinomas and its relation to p53, Ki-67 and prognosis. J Oral Pathol Med 2003;32:552-61.

6. Terhaard CH, Lubsen H, Rasch CR, Levendag PC, Kaaders HH, Tjho-Heslinga RE, van Den Ende PL, Burlage F. The role of radiotherapy in the treatment of malignant salivary gland tumors. Int J Radiat Oncol Biol Phys 2005;61:103-11.