Senescent Tumor Cells Are Frequently Present at the Invasion Front: Implications for Improving Disease Control in Patients with Locally Advanced Prostate Cancer

INTRODUCTION: Local tumor invasion is a critical factor for the outcome of men with prostate cancer. In particular, seminal vesicle invasion (SVI) has been reported to be associated with a more unfavorable prognosis. A better understanding of the functional state of invading prostate cancer cells is crucial to develop novel therapeutic strategies for patients with locally advanced disease. METHODS: The prognostic impact of local tumor progression was ascertained in over 1,000 men with prostate cancer. Prostate cancer specimens were stained by double-immunohistochemistry for the proliferation marker Ki-67 and the senescence marker p16(INK4A). The migratory properties of senescent prostate cancer cells were analyzed in vitro using a wound healing assay and immunofluorescence microscopy for p16(INK4A). RESULTS: We confirm the notion that patients with SVI have a more unfavorable prognosis than patients with extraprostatic extension alone. Surprisingly, we found that the tumor invasion front frequently harbors p16(INK4A)-positive and Ki-67-negative, i.e., senescent, tumor cells. While the intraprostatic tumor periphery was a hotspot for both proliferation and expression of p16(INK4A), the area of SVI showed less proliferative activity but was at the same time a hotspot of cells with increased nuclear p16(INK4A) expression. Senescence was associated with an accelerated migration of prostate cancer cells in vitro. CONCLUSION: This proof-of-concept study shows that invading prostate cancer cells frequently show signs of cellular senescence. This finding may open new avenues for neoadjuvant and adjuvant treatment concepts in men with locally advanced prostate cancer.