title: 'Prechronous' metastasis in clear cell renal cell carcinoma: a case report.
abstract: BACKGROUND
  Although metastatic carcinoma in the presence of an occult primary tumor is well recognized, underlying reasons for the failure of the primary tumor to manifest are uncertain. Explanations for this phenomenon have ranged from spontaneous regression of the primary tumor to early metastasis of the primary tumor before manifestation of a less aggressive primary tumor. We report a case of 'prechronous' metastasis arising from clear cell renal cell carcinoma, where metastatic disease initially manifested in the absence of a primary renal tumor, followed by aggressive growth of the primary renal lesion.
  
  
  METHODS
  A 43-year-old Malay man initially presented to our facility with fever and cough. He subsequently underwent surgical resection of a 9 cm right-sided lung mass found on radiological examination. Histology showed a high-grade clear cell tumor with sarcomatoid differentiation, suggestive of a metastasis from clear cell renal cell carcinoma. However, no concurrent renal lesions were noted on computed tomographic evaluation at that time. Then, four months after lung resection, he presented with a subcutaneous mass in the left loin, as well as right loin discomfort. Computed tomography scanning revealed a 10 cm right renal mass, with renal vein and inferior vena cava invasion, as well as recurrent disease in the right thorax. Histological examination of the excised subcutaneous mass revealed a high-grade carcinoma consistent with clear cell renal cell carcinoma.
  
  
  CONCLUSIONS
  This is the first reported case of prechronous metastasis of renal cell carcinoma, with metastatic disease manifesting prior to the development of the primary lesion. The underlying mechanism is uncertain, but our patient's case provides anecdotal support for the early dissemination model of metastasis.
authors.affiliation: Department of Medical Oncology, National Cancer Centre Singapore. minhan.tan@gmail.com.
authors.forename: Eileen
authors.initials: E
authors.lastname: Poon
authors.forename: Sin Jen
authors.initials: SJ
authors.lastname: Ong
authors.forename: Xue En
authors.initials: XE
authors.lastname: Chuang
authors.forename: Wan Teck
authors.initials: WT
authors.lastname: Lim
authors.forename: Nor Azhari
authors.initials: NA
authors.lastname: Mohd Zam
authors.forename: Tsung Wen
authors.initials: TW
authors.lastname: Chong
authors.forename: Issam
authors.initials: I
authors.lastname: Al Jajeh
authors.forename: Kent
authors.initials: K
authors.lastname: Mancer
authors.forename: Min-Han
authors.initials: MH
authors.lastname: Tan