High cytoplasmic expression of p27 ^Kip1 is associated with a worse cancer-specific survival in clear cell renal cell carcinoma

What's known on the subject? and What does the study add? The loss of p27 ^Kip1 correlates with poor prognosis in various human cancers, and was postulated as a biomarker in RCC. Up to now p27 ^Kip1 analysis in RCC was focused on its nuclear localization. We confirmed higher p27 ^Kip1 expression in the nucleus and cytoplasm of RCC and correlated high cytoplasmic p27 ^Kip1 with an unfavourable clinic and a reduced survival. OBJECTIVES To analyse the cytoplasmic and nuclear differences of p27 ^Kip1 expression and localization in benign and clear cell renal cell carcinoma (ccRCC) with regard to overall survival (OS) and cancer-specific survival (CSS). p27 ^Kip1 is considered to contribute to the progression of ccRCC and is targeted by next generation dual-therapies. PATIENTS AND METHODS In 140 patients, ccRCC and corresponding benign kidney tissue were analyzed for nuclear and cytoplasmic staining of p27 ^Kip1 by immunohistochemistry using a tissue microarray technique. Staining intensity and percentage of positive stained cells are given as expression scores. p27 ^Kip1 expression was categorized as high if ccRCC tissue stained stronger than the respective level of the corresponding benign tissue and categorized as low if ccRCC tissue stained less than or equal to the corresponding benign tissue. Differences in OS and CSS were analyzed by log-rank analysis and expression levels were correlated with tumour and patient characteristics using Fisher's exact test. RESULTS Cytoplasmatic (mean [sd]: 13.8% [1.2%] vs 10.7% [1.7%]; P= 0.04) and nuclear (mean [sd]: 75.6% [2.7%] vs 13.6% [2.1%]; P < 0.001) staining of p27 ^Kip1 were significantly stronger in ccRCC tissues compared to benign tissue. High cytoplasmic p27 ^Kip1 expression was significantly associated with a higher T and N stage, Fuhrman grade and the presence of metastatic disease (P < 0.001). The median follow-up time was 38.2 months. There was no difference in OS between the low and high expression groups, although CSS was significantly lower in patients with high cytoplasmic p27 ^Kip1 (P < 0.001) and CSS heavily tended to be lower in the nuclear low expression group (P= 0.069). CONCLUSIONS High cytoplasmic p27 ^Kip1 levels in renal cancer tissues are associated with advanced disease and reduced cancer specific survival, whereas low nuclear expression levels appear to be beneficial. The present study corroborates the consideration of cytoplasmic p27 ^Kip1 for future diagnostic and targeted therapeutic approaches in RCC establishing a potential protective shift of p27 ^Kip1 from the cytoplasm to the nucleus.