Metastatic Clear Cell Renal Carcinoma Without Evidence of a Primary Renal Tumour Mimicking Advanced Stage of Malignant Lung Tumour.

Background: Clear cell renal carcinoma (ccRC) accounts for 65-70% of renal carcinomas with peak occurrence at the 6th and 7th age decade, predominantly in males. At the time of diagnosis, especially pulmonary metastases can be found in one-third of patients. There have also been described as late metastases for several decades after nephrectomy. In our case report, clinical course indicated primary lung tumour. Histological differential diagnosis included malignant pleural mesothelioma, lung adenocarcinoma and squamous cell carcinoma with clear cell differentiation or primary clear cell adenocarcinoma of the lung. However, using immunohistochemistry, all these possible diagnoses were excluded.

Case Report: We present a case of 62-year old man with 3 months history of progressive dyspnea accompanied with a cough and recurrent pleural effusions. PET/CT scan revealed metastatic tumour spread with right-sided pleural thickening, multiple pulmonary tumour foci, mediastinal, cervical, abdominal para-aortic and pelvic lymph node involvement and skeletal metastasis. The patient died one day after administration of palliative chemotherapy. The autopsy showed the majority of changes in the right hemithorax, was caused by a diffuse yellowish, extremely tough tumour infiltrating parietal and visceral pleura with adhesions and obliteration of truncus pulmonalis. In left lung and both renal cortices we could see scant nodules, mimicking primary lung tumour metastasis. In close proximity to the left renal hilum we found unusual homogeneous white round to oval tissue of 80 × 86 × 72mm in diameter, with identical histological pattern. Extensive immunohistochemical profile (positivity of CK18, PAX8, vimentin, androgen receptor, napsin A; negativity of mesothelial markers, TTF-1, CK7, CK20, CDX-2, CD10, PSA, CK34B12 and PAS-D) was compatible with metastatic ccRC.

Conclusion: We present an extremely rare case of morphologically verified metastatic ccRC without evidence of primary lesion in the kidneys. There is speculated the possibility of spontaneous regression of primary tumour. In our case, however, we cannot exclude the possibility of generalized primary tumour of ectopic kidney. This hypothesis is based on the finding of isolated tumour mass adjacent to left renal hilum.