**3. Pathological and biological similarities between MSGTs and breast cancer**

Mammary and salivary glands are tubulo-acinar exocrine glands that share similar morphological characteristics. Similar histological features are observed when the tumors arising from these 2 sites are compared (Camelo-Piragua et al., 2009; Hellquist et al., 1994; Marchio et al., 2010; Pia-Foschini et al., 2003). Although the cancers differ in terms of their incidence and clinical behavior, certain biological features have been described in both entities and potential common therapeutic approaches have been considered. The WHO classification of MSGTs lists more than 20 different histological subtypes (Laurie et al., 2006; Milano et al., 2007). The majority of these are divided into 2 groups—those of secretory duct origin (including mucoepidermoid carcinoma [MEC] and salivary duct carcinoma [SDC]) and those of intercalated origin (including adenoid cystic carcinoma [ACC]) (Batsakis et al., 1989; Dardick et al., 1987). Most of these tumors occur in the parotid gland (70%), and less than 25% are malignant (Glisson et al., 2004). Although the incidence of tumors at other sites such as the submandibular, sublingual, and minor salivary glands is less common, malignancy at these sites is higher, approximating 50% (Glisson et al., 2004). Most aggressive breast cancers are composed of invasive ductal carcinomas, and other histologic features such as MEC and ACC are relatively rare. Below, we briefly describe some of the types of MSGTs that display features (at the morphological and molecular level) that they have in common with breast cancers, and could therefore provide potential common therapeutic strategies.

#### **3.1 Mucoepidermoid carcinoma (MEC)**

316 Sex Steroids

Tamoxifen, an estrogen receptor antagonist, and a synthetic progestin similar to progesterone, are considered to be effective at inhibiting tumor cell proliferation. These drugs are given as adjuvant therapies to breast cancer patients when immunohistochemical staining of their tumor tissue indicates that >10% of the breast cancer cells express ER or PR (Horwitz, 1993; Williams et al., 2007). Molecular-targeted drug therapy is generally less toxic than traditional chemotherapy; however, some studies have reported severe side effects, and carefully designed and regulated clinical trials are necessary to confirm their safety. Moreover, these types of therapies are not viable when a tumor expresses a low level of a molecular target such as a receptor (Ismail-Khanet al., 2010). This problem is exemplified by breast cancers that do not express ER, PR, or HER2 receptors, that is, in triple negative cases. It is a challenge for clinicians to provide efficacious treatments for this patient population. Sex steroid hormone therapy in prostate cancers is based on their high sensitivity to androgen inhibition. The most common hormone therapy is initiated by reducing the concentration of circulating androgens through surgical or medical castration and/or by administering anti-androgens such as flutamide or bicalutamide (Klotz et al., 2005; Miyake et al., 2005). However, in almost all patients, the efficacy of the treatment decreases over time as the tumor becomes "androgen-refractory" (Yuan et al., 2009). As a result, these patients develop distant metastases, such as in the bone, which eventually proves fatal to the patient. Therefore, the molecular events that control the transition from androgen-sensitive

prostate cancer to androgen-refractory prostate cancer need to be elucidated.

is needed to help drive the development of potential new therapies.

Accumulating evidence suggests that the androgen receptor (AR) plays a critical role in regulating the growth of both androgen-sensitive and androgen-refractory prostate cancer (Chen et al., 2004; Debes et al., 2004; Grossmann et al., 2001; Hara et al., 2003; Scher et al., 2005; Taplin et al., 2004). In addition, recent studies have shown that the AR can regulate invasion and metastasis (Hara et al., 2008). In AR-negative cell lines such as PC3 and DU145, it has been shown that forced AR expression decreases their invasive properties and treatment with androgen further reduces invasion by these cells (Bonaccorsi et al., 2000; Cinar et al., 2001). Moreover, it has been reported that hormone-refractory prostate cancers have a variety of AR alterations that are either not found in hormone-naive tumors or are found at a lower frequency (Taplin et al., 2004). A more recent investigation demonstrated that forced expression of AR in a subline of a metastatic androgen-dependent prostate cancer cell line led to increased invasion (Hara et al., 2008). It is clear that a more detailed understanding of the AR alterations in the evolution of androgen-refractory prostate cancer

Few studies of ovarian and colon cancer have addressed the potential application of hormone therapies (Burkman, 2002). In ovarian cancer, the use of estrogen as a menopausal therapy has frequently been associated with an increased risk of ovarian cancer, and there is still conflicting evidence regarding the impact of hormone therapy in terms of decreasing the risk of cancer (Greiser et al., 2010). A recent study, however, suggested that this problem can be circumvented by co-administering progestin and estrogen (Pearce et al., 2009). Further, experiments in culture showed that progesterone reduced the proliferation of both benign and malignant ovarian tumor cells (Zhou et al., 2002). Therefore, progestin might be a key factor for preventing and suppressing ovarian cancer cell growth. In contrast to ovarian cancer, estrogen appears to have protective effects against colon cancer (Kennelly et al., 2008). However, the role of hormone replacement therapy with estrogen for the

treatment of colon cancer is poorly understood, and further analyses are needed.

MEC is the most common salivary gland neoplasm, accounting for 29–34% of all malignancies of the major and minor salivary glands (Milano et al., 2007). These tumors grow slowly and present as painless masses in most cases. They are primarily composed of intermediate, mucous, and epidermoid cells. The cell types are classified histologically as low-, intermediate-, and high-grade; 5-year overall survival (OS) varies from 92% to 100% for low-grade tumors, 62% to 92% for intermediate-grade tumors, and 0% to 43% for highgrade tumors (Pires et al., 2004). High-grade MEC is an aggressive malignancy, characterized by high rates of local recurrence and distant metastasis. On the contrary, lowgrade MECs generally do not metastasize. MEC of the breast is a rare entity with an estimated incidence of 0.2% and is composed of a mixture of basaloid, intermediate, epidermoid, and mucinous cells (Camelo-Piragua et al., 2009; Fisher et al., 1983). Since Patchefsky et al. first described breast MEC in 1979, only 28 cases have been reported (Berry et al., 1998; Chang et al., 1998; Di Tommaso et al., 2004; Fisher et al., 1983; Gomez-Aracil et al., 2006; Hanna et al., 1985; Hastrup et al., 1985; Hornychova et al., 2007; Kovi et al., 1981; Leong et al., 1985; Luchtrath et al., 1989; Markopoulos et al., 1998; Patchefsky et al., 1979; Pettinato et al., 1989; Ratanarapee et al., 1983; Tjalma et al., 2002). Because of its rarity, the prognosis remains controversial debatable matter. However, MECs from the breasts and salivary glands have been shown to share similar biological features and morphologies (Camelo-Piragua et al., 2009). Researchers have classified breast MECs into 3 grades by using the same grading system as for salivary gland tumors and have demonstrated that high-grade tumors are associated with high mortality as a result of lymph node and distant metastases. These results suggest that MECs from both mammary and salivary glands have similar morphological features, and thus could have similar treatment strategies. Further, a common cytogenetic alteration of breast and salivary MECs has been reported. A reciprocal

Hormone Therapy for the Treatment of Patients with Malignant Salivary Gland Tumor (MSGT) 319

variety of molecular studies have led to the identification of certain biological markers of SDCs. Among these is HER-2, which is amplified in 20–25% of breast cancers (Moy et al., 2006; Press et al., 1997). Various studies of HER-2 in SDC have shown variable results, with amplification occurring in 25–100% of tumors (Jaspers et al., 2011). Nonetheless, the proportion is much higher than that observed in the other histological subtypes, such as the ACCs and MECs described above (Etges et al., 2003; Giannoni et al., 1995; Gibbons et al., 2001; Glisson et al., 2004; Hellquist et al., 1994; Jaehne et al., 2005; Locati et al., 2009; Milanoet al., 2007; Nguyen et al., 2003; Press et al., 1994; Skalova et al., 2001; Williams et al., 2007). HER-2 expression is considered to correlate with histological grade in both salivary gland neoplasms as well as breast cancer, and represents a potential attractive therapeutic approach for SDCs. Since HER-2 can also enhance AR function, anti-androgen therapy may

Previous studies have shown that high EGFR expression in SDCs may contribute to tumor growth (Fan et al., 2001; Locati et al., 2009). EGFR has also been shown to enhance tumorigenesis in several human carcinomas by blocking apoptosis and promoting angiogenesis (Kari et al., 2003). An interaction between both EGFR and HER-2 and hormonal pathways has also been described. In breast and uterine cancers, treatment with anti-EGF antibodies reduces tumor proliferation induced by treatment with estradiol. Likewise, the antiestrogen ICI 164,384 reduces the effects of EGF-induced tumor

Hoang et al. performed molecular studies with microsatellite markers and DNA flow cytometry to compare the biological characteristics of SDC and IDC. They found that there were similar allelic alterations on chromosomal arms 6q, 16q, 17p, and 17q, and DNA aneuploidy in both malignancies; these alterations may contribute to the aggressive behavior (Hoang et al., 2001). Recently, polysomy of chromosome 7 was detected in 25% of SDCs, and this alteration correlated with poor OS (Williams et al., 2010). This correlation was also reported in IDCs, and supports the notion that EGFR gene mutations may guide therapy (Shien et al., 2005). Taken together, gene alterations of both EGFR and HER-2 may define the molecular features of these 2 types of malignancies, and these receptors may be

As described above, several types of MSGTs are morphologically and biologically similar to malignant breast cancers (Pia-Foschini et al., 2003; Wick et al., 1998) (Fig. 1). Further, the clinical significance of sex hormone receptors has been debated since White and Garcelon first described therapy with estrogen against salivary gland neoplasms in 1955 (White & Garcelon, 1955). Previous reports obtained using a low number of biopsy samples have shown conflicting results regarding the expression of sex hormone receptors, making it difficult to determine the potential benefits of hormone therapy (Barnes et al., 1994; Barrera et al., 2008; Dimery et al., 1987; Dori et al., 2000; Jeannon et al., 1999; Lamey et al., 1987; Lewis et al., 1996; Miller et al., 1994; Nasser et al., 2003; Pires et al., 2004; Shick et al., 1995). Therefore, additional studies are required in order to clarify the role of hormone receptors in MSGTs. Although several studies have examined ER and PR expression in MSGTs, there is substantial disparity in the results: the expression of ER and PR varies from 0 to 86% and 0 to 50%, respectively (Barnes et al., 1994; Barrera et al., 2008; Dimery et al., 1987; Dori et al., 2000; Jeannon et al., 1999; Lamey et al., 1987; Lewis et al., 1996; Miller et al., 1994; Nasser et

**4. Hormone therapy for the treatment of patients with MSGTs** 

be effective against MSGTs when HER-2 is overexpressed.

proliferation (Shupnik, 2004).

candidates for targeted therapy.

translocation t(11;19)(q21;p13) (MAML2: MECT) was identified in breast MEC; this is the most frequent genetic alteration in the salivary glands (Tonon et al., 2003). The translocation creates a fusion product (MAML2: MECT1) that activates transcription of cAMP/CREB target genes (Tonon et al., 2003; Tonon et al., 2004). Another report noted that patients in whom the protein fusion gene is expressed have a significantly lower risk of death compared to patients without the fusion protein MAML2:MECT1 (Behboudi et al., 2006). It has also been shown that other subtypes of breast cancer are negative for this gene, suggesting that this fusion gene is specific to MEC. This translocation is likely to be a promising marker of MECs from both the mammary and salivary glands (Nordkvist et al., 1994).

#### **3.2 Adenoid cystic carcinoma (ACC)**

ACCs account for 22% of MSGTs (Hotte et al., 2005). There are 3 histological subtypes: tubular; cribriform; and solid (Da Silva et al., 2009; Pia-Foschini et al., 2003). In contrast to the squamous cell carcinomas that account for the vast majority of head and neck malignancies, ACC often spreads systemically, especially to the lung and bone, and the metastatic proportion of this type of neoplasm is 24–55% (Dodd et al., 2006). Because of the high metastatic rate, prognosis is poor. The 10-year OS is 39–55% and the 20-year OS is 21– 25% (Dodd et al., 2006).

On the other hand, breast ACC is a rare malignancy, accounting for 0.1–1% of all breast cancers (Marchio et al., 2010). In addition, these neoplasms show different clinical behaviors than their salivary gland counterparts. The 10-year OS is >90%, and lymph node and distant metastases are generally rare (Marchio et al., 2010). However, the histological features of breast ACCs are very similar to ACCs originating from the salivary glands (as shown in Fig. 1). Ro et al. applied the same grading system to ACCs from both types of tissues, and both breast and salivary gland tumors are characterized by expression of c-KIT and share a common chromosomal translocation t(6;9) leading to the fusion gene MYB-NFIB (Marchio et al., 2010; Persson et al., 2009; Ro et al., 1987). c-KIT has been shown to be expressed in 80– 100% of ACCs of the salivary glands and in almost all ACCs from the breast (Azoulay et al., 2005; Crisi et al., 2005; Edwards et al., 2003; Holst et al., 1999; Jeng et al., 2000; Mastropasqua et al., 2005; Vila et al., 2009; Weigelt et al., 2008). The genetic alteration t(6;9)(q22-23;p23-24) was first identified as a characteristic of salivary gland ACCs (Nordkvist et al., 1994). Since then, the same translocation has been detected in breast tumors (Persson et al., 2009). The fusion gene is highly expressed in proliferating cells and is downregulated as the cells become more differentiated. Therefore, this gene may provide new therapeutic approaches for the management of ACCs.

#### **3.3 Salivary duct carcinoma (SDC)**

SDC is a rare and highly aggressive neoplasm with histologic features very similar to that of invasive ductal carcinoma of the breast (IDC) (Barneset al., 1994; Hellquist et al., 1994; Kleinsasser et al., 1968). SDC is generally more aggressive and has lower survival rates than other MSGTs. The epithelium tends to form cribriform, papillary, and solid growth patterns along with duct-like structures (Hellquist et al., 1994). The morphology of SDC is characterized by cuboidal and polygonal cells forming distended ducts and solid nests (often with central necrosis) that are very similar to comedocarcinoma (Hellquist et al., 1994). In addition to the histopathological resemblance, both entities have similar clinical behaviors, that is, they have highly metastatic features leading to a poor prognosis. A wide

translocation t(11;19)(q21;p13) (MAML2: MECT) was identified in breast MEC; this is the most frequent genetic alteration in the salivary glands (Tonon et al., 2003). The translocation creates a fusion product (MAML2: MECT1) that activates transcription of cAMP/CREB target genes (Tonon et al., 2003; Tonon et al., 2004). Another report noted that patients in whom the protein fusion gene is expressed have a significantly lower risk of death compared to patients without the fusion protein MAML2:MECT1 (Behboudi et al., 2006). It has also been shown that other subtypes of breast cancer are negative for this gene, suggesting that this fusion gene is specific to MEC. This translocation is likely to be a promising marker of MECs from both the

ACCs account for 22% of MSGTs (Hotte et al., 2005). There are 3 histological subtypes: tubular; cribriform; and solid (Da Silva et al., 2009; Pia-Foschini et al., 2003). In contrast to the squamous cell carcinomas that account for the vast majority of head and neck malignancies, ACC often spreads systemically, especially to the lung and bone, and the metastatic proportion of this type of neoplasm is 24–55% (Dodd et al., 2006). Because of the high metastatic rate, prognosis is poor. The 10-year OS is 39–55% and the 20-year OS is 21–

On the other hand, breast ACC is a rare malignancy, accounting for 0.1–1% of all breast cancers (Marchio et al., 2010). In addition, these neoplasms show different clinical behaviors than their salivary gland counterparts. The 10-year OS is >90%, and lymph node and distant metastases are generally rare (Marchio et al., 2010). However, the histological features of breast ACCs are very similar to ACCs originating from the salivary glands (as shown in Fig. 1). Ro et al. applied the same grading system to ACCs from both types of tissues, and both breast and salivary gland tumors are characterized by expression of c-KIT and share a common chromosomal translocation t(6;9) leading to the fusion gene MYB-NFIB (Marchio et al., 2010; Persson et al., 2009; Ro et al., 1987). c-KIT has been shown to be expressed in 80– 100% of ACCs of the salivary glands and in almost all ACCs from the breast (Azoulay et al., 2005; Crisi et al., 2005; Edwards et al., 2003; Holst et al., 1999; Jeng et al., 2000; Mastropasqua et al., 2005; Vila et al., 2009; Weigelt et al., 2008). The genetic alteration t(6;9)(q22-23;p23-24) was first identified as a characteristic of salivary gland ACCs (Nordkvist et al., 1994). Since then, the same translocation has been detected in breast tumors (Persson et al., 2009). The fusion gene is highly expressed in proliferating cells and is downregulated as the cells become more differentiated. Therefore, this gene may provide new therapeutic approaches

SDC is a rare and highly aggressive neoplasm with histologic features very similar to that of invasive ductal carcinoma of the breast (IDC) (Barneset al., 1994; Hellquist et al., 1994; Kleinsasser et al., 1968). SDC is generally more aggressive and has lower survival rates than other MSGTs. The epithelium tends to form cribriform, papillary, and solid growth patterns along with duct-like structures (Hellquist et al., 1994). The morphology of SDC is characterized by cuboidal and polygonal cells forming distended ducts and solid nests (often with central necrosis) that are very similar to comedocarcinoma (Hellquist et al., 1994). In addition to the histopathological resemblance, both entities have similar clinical behaviors, that is, they have highly metastatic features leading to a poor prognosis. A wide

mammary and salivary glands (Nordkvist et al., 1994).

**3.2 Adenoid cystic carcinoma (ACC)** 

25% (Dodd et al., 2006).

for the management of ACCs.

**3.3 Salivary duct carcinoma (SDC)** 

variety of molecular studies have led to the identification of certain biological markers of SDCs. Among these is HER-2, which is amplified in 20–25% of breast cancers (Moy et al., 2006; Press et al., 1997). Various studies of HER-2 in SDC have shown variable results, with amplification occurring in 25–100% of tumors (Jaspers et al., 2011). Nonetheless, the proportion is much higher than that observed in the other histological subtypes, such as the ACCs and MECs described above (Etges et al., 2003; Giannoni et al., 1995; Gibbons et al., 2001; Glisson et al., 2004; Hellquist et al., 1994; Jaehne et al., 2005; Locati et al., 2009; Milanoet al., 2007; Nguyen et al., 2003; Press et al., 1994; Skalova et al., 2001; Williams et al., 2007). HER-2 expression is considered to correlate with histological grade in both salivary gland neoplasms as well as breast cancer, and represents a potential attractive therapeutic approach for SDCs. Since HER-2 can also enhance AR function, anti-androgen therapy may be effective against MSGTs when HER-2 is overexpressed.

Previous studies have shown that high EGFR expression in SDCs may contribute to tumor growth (Fan et al., 2001; Locati et al., 2009). EGFR has also been shown to enhance tumorigenesis in several human carcinomas by blocking apoptosis and promoting angiogenesis (Kari et al., 2003). An interaction between both EGFR and HER-2 and hormonal pathways has also been described. In breast and uterine cancers, treatment with anti-EGF antibodies reduces tumor proliferation induced by treatment with estradiol. Likewise, the antiestrogen ICI 164,384 reduces the effects of EGF-induced tumor proliferation (Shupnik, 2004).

Hoang et al. performed molecular studies with microsatellite markers and DNA flow cytometry to compare the biological characteristics of SDC and IDC. They found that there were similar allelic alterations on chromosomal arms 6q, 16q, 17p, and 17q, and DNA aneuploidy in both malignancies; these alterations may contribute to the aggressive behavior (Hoang et al., 2001). Recently, polysomy of chromosome 7 was detected in 25% of SDCs, and this alteration correlated with poor OS (Williams et al., 2010). This correlation was also reported in IDCs, and supports the notion that EGFR gene mutations may guide therapy (Shien et al., 2005). Taken together, gene alterations of both EGFR and HER-2 may define the molecular features of these 2 types of malignancies, and these receptors may be candidates for targeted therapy.
