Page 89 - New epidemiological and PSMA-expression based paradigms in salivary gland tumors

Risk of breast cancer after a salivary gland tumor in the Netherlands
this could also explain the reported female preponderance of SGC and SGPA. In the literature, generally only a small portion of salivary gland tumors show ER-overexpression based on immunohistochemistry, possibly because mainly ER-α and not ER-β expression status has been assessed[45–51]. Nevertheless, although ER-β expression in salivary gland tumors was only reported in a limited number of series, ER-β was overexpressed in 27 of 38 (71%) patients in a series of adenoid cystic carcinomas and in 57 of 80 (73%) in a series of salivary duct carcinomas[16,52].
In SGPA and adenoid cystic carcinoma, the slight, but relevant difference in incidence between males and females (female to male incidence ratio of 1.4:1 and 1.2:1, respectively) and the overexpression of estrogen β receptor (ER-β), compared to normal salivary gland, may suggest a role for the proliferative influence of estrogens in tumorigenesis[2,14,53]. Similar considerations have been mentioned in earlier reports of experimental anti-estrogen treatment for SGC in the literature [8,54,55]. From the above, it could be concluded it is a realistic possibility that estrogens play a role in the association between salivary gland tumors and BC.
Salivary gland tumor treatment or metastasis: It is unlikely that SGC of SGPA treatment contributes to an increased BC risk since locoregional treatment does not affect breast tissue. In external beam radiotherapy for SGC, the breast is not an organ at risk due to the direct dose, although scattered radiation could in theory add to the risk of primary breast cancer. This dose can be calculated. After radiotherapy for SGC in the earlier mentioned example of a 50-year old female patient, this estimated additional lifetime risk is 0.3%, for all cancers. So, scattering does not contribute substantially to the risk of BC.
An increased BC risk due to SGC chemotherapy (depending on histology, but mostly cisplatin based) is not very likely[56,57]. Solitary metastasis of SGC to the breast is not very likely. The SGPA is known to almost never metastasize at all. Also, if there were cases, these would probably have been recorded in the pathology database or cancer registry not as BC but as metastasized salivary gland tumor. Common genetic susceptibility: Germline mutations that could account for the occurrence of both a salivary gland tumor and BC in the same woman have not been identified yet, and the literature on this topic is limited. One retrospective study including 5,754 proven or likely carriers from 187 BRCA1 or BRCA2 positive
5
87