Metastatic lesions to the oral cavity from distant tumors are uncommon, accounting for only 1% of all oral malignancies. They mainly involve the bony structures (particularly the mandible), whereas primary metastases to soft tissues are extraordinarily rare (only 0.1% of oral malignancies). The most common sites of soft tissue involvement are the gingiva, tongue, lips and the buccal and palatal mucosa. The primary tumors are mainly lung, breast, kidney and colon.[3
Prostate cancer metastasizing to soft tissues in the oral cavity as a presenting feature has been anecdotally reported in the surgical literature.[2
] But gingivum had been the site described – it may be the extension of bone metastasis involving the jaw bones. Diagnosis requires a high index of suspicion especially if the predominant presentation is oral cavity lesion. Immunohistochemistry with prostate-specific antigen (PSA) – and prostate-specific acid phosphatase (PSAP) would be helpful.
Prostate-specific antigen is a 30-kDa glycoprotein serine protease that shows high tissue specificity for prostatic tissue, both benign and malignant. However, recent reports have shown that a variety of normal and neoplastic tissue types express PSA immunohistochemically. One diagnostic pitfall is the localization of PSA-like immunoreactivity in human salivary glands. This is usually seen in the apical cytoplasm along the luminal border of small-sized duct epithelial cells of major salivary (parotid and submandibular) glands of both sexes.[4
] However, in large-sized duct epithelial cells, acinar cells and minor salivary gland ducts it may be negative. Since our patient had a histologically proven prostate cancer, it suggests the oral lesion to be metastatic from the prostate.
Recently, studies have demonstrated that FDG-PET scanning may in fact play an important role in the evaluation of advanced androgen-independent disease and in staging and evaluation of response to hormonal manipulations in high-risk localized and locally advanced prostate cancers.[5
] So in future FDG-PET may be helpful in detecting these rare metastatic sites ante mortem.
Metastastic prostate cancer carries poor prognosis and how the ante mortem diagnosis of these unusual metastatic sites dictates management and prognosis is largely unknown. Management strategies remain the same essentially. Castration, surgical or medical, is the standard of care. Hormonal manipulation does not always result in a favorable response. The degree of differentiation may be a good prognostic indicator in this regard. However, no large experience exists in the literature in treating such cases.