Introduction
Prostate cancer is the most common cancer among men in Western countries. The 5-year survival rate of localized and regional prostate cancer is ~100%, whereas that of metastatic prostate cancer is only 27–28% (1). As serum prostate-specific antigen (PSA) screening has become widespread, the proportion of cases presenting with lymph node involvement or advanced disease has decreased considerably (2). However, ~20% of patients present with metastatic disease. Metastatic prostate cancer usually involves the pelvic lymph nodes, bones, and lungs (2), with bone pain being a common symptom in SUCH patients. However, there are other rare manifestations of metastatic prostate cancer. HereIN, we present a rare case of prostate cancer metastasis initially presenting as chylothorax.
Case report
A 64-year-old Asian man visited the emergency room with dyspnea. The patient's medical history was unremarkable, with the exception of being a current smoker with a 20 pack-year history. Radiographic images, including computed tomography scan of the chest, revealed a left pleural effusion, pericardial effusion, and enlarged lymph nodes in the left supraclavicular/posterior neck/axillary area, right upper paratracheal area, subcarinal area, and bilateral lower paratracheal areas (Fig. 1A and B). Thoracentesis was performed and fluid analysis revealed a chylothorax, in which the triglyceride level was 244 mg/dl (normal range, <50 mg/dl). Whole-body lymphoscintigraphy revealed faint tracer accumulation activity in the medial portion of the left hemithorax, where the pleural effusion was present (Fig. 1C). Considering that the patient had never received thoracic surgery or experienced trauma, malignancy was suspected. Pleural fluid cytology revealed numerous mononuclear leukocytes and some reactive mesothelial cells, but did not show any evidence of malignancy. The serum PSA level was elevated to 194.6 ng/ml (normal range, 0–3 ng/ml).
A prostate biopsy revealed adenocarcinoma of the prostate gland. A bone scan was performed for staging, which revealed multiple bone metastases (Fig. 1D). Therefore, the chylothorax was considered to have resulted from thoracic duct obstruction by enlarged lymph node metastasis from prostate cancer. Androgen deprivation therapy (ADT) was initiated, with simultaneous administration of goserelin and anti-androgen. After 3 months, the amount of pleural effusion had decreased (Fig. 2A) and the serum PSA level decreased from 194.6 to 31.68 ng/ml following ADT. A bone scan performed 8 months after the initiation of ADT revealed that the intensities of multiple bone uptakes had decreased significantly when compared to the initial scan (Fig. 2B). The patient is undergoing regular follow-up at our outpatient clinic for 1 year after diagnosis and has not reported experiencing any further discomfort.
Discussion
In Korea, among males aged ≥65 years, prostate cancer is the fourth most common type of cancer and its incidence is increasing with advancing age. The crude mortality of prostate cancer is 2.8/10,000 and the 5-year relative survival rate by year of diagnosis from 2007–2011 was 92%, indicating that it is a highly treatable cancer (3).
There is some controversy regarding the efficacy of serum PSA screening. Randomized trials have demonstrated that serum PSA screening reduces metastatic prostate cancer incidence and disease-related mortality (4). However, other STUDIEs have reported that, due to the unnecessary biopsies following false-positive serum PSA results, cancer risk-adapted serum PSA screening is required (5). In the United States, the proportion of patients presenting with metastatic disease decreased from 17% in 1988–1990 to 4% in 1996-1998, while the proportion presenting with stage T1 tumors conversely increased from 14 to 51% (6).
As stated above, metastatic prostate cancer usually involves the pelvic lymph nodes, bones and lungs (2) and it may present as a skin lesion, endobronchial mass, ascites, or renal mass. Table I summarizes some of the rare manifestations of prostate cancer (7–19). Although our patient was not the first case of metastatic prostate cancer presenting as chylothorax, initial presentation of prostate cancer as chylothorax is quite rare (18,19).
Lymphoscintigraphy, which functionally assesses the lymphatic transport and regional lymph nodes, is an easy, non-invasive method for detecting abnormalities in the lymphatic system, including leakages such as chylothorax, chyloperitoneum and chyluria. Positive findings include tracer activity at the site where lymphatic fluid is accumulated, as seen in our case (20,21). ADT is the mainstay of treatment for patients with metastatic prostate cancer. Luteinizing hormone-releasing hormone agonists have become the standard of care in hormonal therapy, as these agents have the potential of reversibility and enable the use of intermittent androgen deprivation (22). Moreover, with ADT, patients avoid the physical and psychological discomfort associated with orchiectomy (23). Intermittent androgen deprivation alternates androgen blockade with treatment cessation, in order to allow hormonal recovery between the treatment cycles, thus potentially improving the tolerability and quality of life. Hence, for older patients, intermittent androgen deprivation may generally be applied (24).
In summary, chylothorax is an uncommon condition. If there is no history of chest/neck injury or surgery, exclusion of malignancy is crucial. Despite its low probability, prostate cancer with mediastinal lymph node metastasis may result in chylothorax. Therefore, when we evaluate the causes of non-traumatic chylothorax, prostate cancer should be considered, and serum PSA screening is recommended to exclude this possibility.