At the time of diagnosis, 30% of kidney cancers are metastatic [4]. In 95% of cases, it is a polymetastatic tumor disease [5] .
RCC is characterized by a high metastatic potential [6] generating renal metastases before there are clinical signs of renal disease in 30% of patients [7].
The metastatic spread of carcinomatous renal cells may involve lymphogenous, lymphohematogenous and hematogenous routes. Sometimes, the metastatic sites are unusual, generating puzzling clinical manifestations [7].
This tumor commonly metastasizes haematogenously via renal veins [8] .
Multiples lung nodules is the most common form of thoracic metastasis. Metastatic invasion of the pleura may occur in 12% of cases [9]. It can be accessible to biopsy such in the case of our patient.
ccRCC is known to be the most common histological subtype of RCC [10] .
Microscopically, architecture is acinar, nested, cords, tubular, and alveolar. Some of the lumens are larger, forming microscopic cysts of variable size. Neoplastic cells are cuboidal cells with typical optically cleared cytoplasm containing glycogen and lipid droplets.
ccRCCs are richly vascularized and have a delicate network of capillary vessels. Tumor may have calcifications with hemorrhage and/or necrotic areas [11] .
ccRCC in the pleura can pose differential diagnoses with metastases from ovarian clear cell carcinoma, endometroid carcinoma with clear cell carcinoma and chromophobe renal cell carcinoma. On immunohistochemical study, ccRCC is usually positive for cluster of differentiation 10 (CD10), cytokeratins AE1/AE3, EMA, vimentin and CAM5.2 but negative for CK7 and CK20 [12] .
Another rare metastatic location of kidney cancer is the pancreas. However, this organ is more frequently affected compared to the other viscera of the digestive tract [13].
The clinical expression of this metastatic tumor invasion is polymorphic. In the meta-analysis conducted by Sellner et al including 236 cases of renal tumor metastasizing to the pancreas, 35% of these patients had no symptoms. The symptomatic forms are mainly abdominal pain (20%), gastrointestinal bleeding (20%), jaundice (9%) and pancreatitis (3%). Diabetes was found in 3% of patients [14].
Cancer cells can also engraft into the contralateral kidney. Bianchi et al studied the metastatic sites distribution of mRCC. The other kidney was involved in 1.4% of these secondary lesions [15].
To rationalize the choice of therapeutic option, prognostic evaluation is necessary. The two prognostic classifications adopted for the RCC are those of Heng and IMDC [16].
For patients with poor prognosis, as is the case in our observation, anti-angiogenic treatment is recommended.
The median overall survival of patients with mRCC in the poor prognosis group is 8 months [17] .
Our study highlights the significant challenges in diagnosing patients with renal cancer.
The main limitation of our study is the short follow-up period.