Determination of enzalutamide long-term safety and efficacy for castration-resistant prostate cancer patients after combined anti-androgen blockade followed by alternative anti-androgen therapy: a multicenter prospective DELC study.

BACKGROUND: Alternative anti-androgen therapy has been widely used as a first-line treatment for castration-resistant prostate cancer, and it may affect treatment outcome of subsequent agents targeting the androgen receptor axis. We conducted the prospective observational DELC (Determination of Enzalutamide Long-term safety and efficacy for Castration-resistant prostate cancer patients after combined anti-androgen blockade followed by alternative anti-androgen therapy) study to evaluate the efficacy of enzalutamide in patients with castration-resistant prostate cancer who underwent prior combined androgen blockade with bicalutamide and then alternative anti-androgen therapy with flutamide. METHODS: The DELC study enrolled 163 Japanese patients with castration-resistant prostate cancer who underwent alternative anti-androgen therapy with flutamide following failure of initial combined androgen blockade with bicalutamide in multiple institutions between January 2016 and March 2019. Primary endpoint was overall survival. Administration of enzalutamide was started at 160 mg orally once daily in all patients. RESULTS: The rate of decline of prostate-specific antigen by 50% or more was 72.2%, and median overall survival was 42.05 months. Multivariate analysis revealed that higher pretreatment serum levels of prostate-specific antigen (≥11.3 ng/mL; P = 0.004), neuron-specific enolase (P = 0.014) and interleukin-6 (≥2.15 pg/mL; P = 0.004) were independent risk factors for overall survival. Fatigue (30.0%), constipation (19.6%) and appetite loss (17.8%) were the most common clinically relevant adverse events. The enzalutamide dose was not reduced in any patient under the age of 70, but adherence was decreased in those over 70. CONCLUSIONS: In the DELC study, the safety of enzalutamide was comparable to that in previous reports. Serum levels of neuron-specific enolase and interleukin-6 were suggested as prognostic factors for castration-resistant prostate cancer with potential clinical utility.

A comparative study on nivolumab and axitinib as secondary treatment in patients with metastatic renal cell carcinoma: A multi-institutional retrospective study in Japan.

OBJECTIVES: When primary treatment has been inadequate, nivolumab and axitinib are often used as a secondary treatments for patients with metastatic renal cell carcinoma (mRCC). However, there have been few reports comparing the efficacy and safety of these drugs. METHODS: We retrospectively investigated 58 patients treated with nivolumab and 57 patients treated with axitinib as secondary treatment between April 2013 and December 2019. We then assessed the clinical efficacy and safety of the treatments in both groups. RESULTS: The most common primary therapy was sunitinib (61.7%). Both nivolumab and axitinib groups showed no significant differences in terms of the objective response rate and disease control rate (p = 0.280 and p = 0.518, respectively). Importantly, progression-free survival (PFS) and overall survival (OS) seemed to be similar in patients treated with nivolumab and axitinib (p = 0.527 and p = 0.266, respectively), irrespective of the objective response to primary therapy. Furthermore, a Cox proportional hazards model showed that pretreatment Karnofsky Performance Status was significantly associated with PFS and OS. Although the incidence of adverse events was significantly higher in the patients treated with axitinib, there was no significant difference in time to treatment failure between the two groups. CONCLUSIONS: Nivolumab and axitinib showed similar clinical benefits as secondary treatment in patients with mRCC; thus, they should be an option in sequential therapy following treatment with tyrosine kinase inhibitors (TKIs). Future studies and feasible therapeutic biomarkers would help predict the clinical response to TKIs or immune checkpoint inhibitors in patients with mRCC.

[A Case of Prostate Cancer Diagnosed by the Bone Biopsy of the Right Iliac Metastatic Lesion].

A 73-year-old man was referred to our hospital because of a high prostate specific antigen (PSA) level. The PSA level at our hospital was 63.5 ng/ml. Pelvic magnetic resonance imaging (MRI) showed findings strongly suggestive of multiple pelvic bone metastases, but no obvious malignant findings in the prostate. A 12-core prostate biopsy was performed and no cancer was detected. Computed tomography and bone scintigraphy showed findings suspicious of bone metastases in the sternum, thoracolumbar spine, pelvic bone, and sacrum. Spine MRI revealed a mass in the vertebral body from the eighth thoracic vertebra to the first lumbar vertebra. A biopsy of the right iliac crest showed adenocarcinoma and was positive for PSA staining, leading to the diagnosis of multiple bone metastases of prostate cancer. Abiraterone acetate in combination with androgen deprivation was started. He received medication and radiation therapy to his sternum for pain relief. Spine MRI after 4 months showed decreased vertebral body weights and serum PSA levels were ＜0.003 ng/ml after 5 months. Seventeen months after treatment, PSA remains below 0.003 ng/ml, and the patient is currently pain-free.

Pilot study of an artificial intelligence-based deep learning algorithm to predict time to castration-resistant prostate cancer for metastatic hormone-naïve prostate cancer.

The object in this study is to develop an artificial intelligence-based deep learning algorithm for prediction of time to castration-resistant prostate cancer by combined androgen blockade therapy in metastatic hormone-naïve prostate cancer. We included 180 metastatic hormone-naïve prostate cancer patients who initially received combined androgen blockade. We first evaluated whether time to castration-resistant prostate cancer was a significant prognostic factor. Then, using the patients' needle-biopsy specimen images, we developed and validated our deep learning algorithm. The results are shown below. First, we confirmed that time to castration-resistant prostate cancer correlated with overall survival (P < 0.001). Next, we selected two groups by time to castration-resistant prostate cancer of >24 months (n = 18) and <6 months (n = 6) and developed a deep learning algorithm by artificial intelligence-based machine deep learning. In 16 other metastatic hormone-naïve prostate cancer patients used as an external validation set, we confirmed the prediction accuracy remained significant (P < 0.05). In conclusion, our obtained deep learning algorithm has high predictive ability for the effectiveness of combined androgen blockade.

Real-world efficacy and safety of nivolumab plus ipilimumab in untreated metastatic renal cell carcinoma, and the impact of previous nephrectomy on clinical outcome: Japanese multi-institutional retrospective study.

BACKGROUND: In metastatic renal-cell carcinoma (mRCC), recent clinical trials have shown efficacy of first-line combination therapy, as evidenced by better clinical outcome over target therapy. However, there are insufficient real-world evidences in mRCC patients in Japan. METHODS: We performed a multicenter retrospective study of 72 mRCC patients who received nivolumab plus ipilimumab as first-line treatment between September 2018 and July 2021. Patient's characteristics, clinical outcomes and safety were retrospectively reviewed. We analyzed overall response rate (ORR), disease control rate (DCR), progression-free survival (PFS), and overall survival (OS) in patients treated with combination therapy. RESULTS: Of all patients, the median age was 70 years (range, 36-86) and the major type of histology was clear cell RCC (n = 55; 76.4%). Progressive disease (n = 25; 34.8%) and irAEs (n = 22; 30.6%) were the most common causes for discontinuing treatment. Median PFS and OS seemed similar between patients who discontinued treatment because of irAEs and for patients who did not (p = 0.360 and p = 0.069, respectively). Importantly, for patients with synchronous metastatic disease at diagnosis (n = 56), nephrectomy before initiating nivolumab plus ipilimumab had a significantly positive impact on better OS when compared to that in patients without nephrectomy (p = 0.028). CONCLUSION: This study confirms efficacy and safety of nivolumab plus ipilimumab for mRCC patients in real-world settings. Furthermore, nivolumab plus ipilimumab was associated with a better outcome in patients who had undergone nephrectomy at diagnosis for synchronous mRCC.

The prognostic impact of immune-related adverse events in metastatic renal cell carcinoma patients treated with nivolumab: a real-world multi-institutional retrospective study.

BACKGROUND: Recent studies have shown that immune-related adverse events (irAEs) caused by immune checkpoint inhibitors (ICIs) were correlated with favorable clinical outcome in patients with melanoma. However, in metastatic renal cell carcinoma (mRCC) patients, there have been few reports about the correlation between irAEs and clinical efficacy of anti-programmed cell death protein-1 (PD-1) therapy. METHODS: We retrospectively investigated 160 mRCC patients who started nivolumab monotherapy between September 2016 and July 2019. IrAEs were defined as patients' AEs having a potential immunological basis that required close follow-up, or immunosuppressive therapy. We compared the data of patients who received nivolumab into two groups based on the occurrence of irAEs and assessed clinical efficacy in both groups. RESULTS: Of all mRCC patients, 47 patients (29.4%) developed irAEs. In patients who developed irAEs, the objective response rate and disease control rate were 38.8% and 77.6%, which were significantly higher when compared to that in patients without irAEs (p = 0.012 and p < 0.001, respectively). Furthermore, the incidence of irAEs was significantly associated with an increase in progression-free survival (PFS) [Hazard ratio (HR) = 0.4867; p = 0.0006] and overall survival (OS) (HR = 0.526; p = 0.0252). Importantly, PFS and OS seemed to be similar in patients who discontinued treatment because of irAEs and in those who did not discontinue because of irAEs (p = 0.36 and p = 0.35, respectively). CONCLUSION: Development of irAEs strongly correlates with clinical benefit for mRCC patients receiving nivolumab monotherapy in real-world settings.

High performance of 5-aminolevulinic acid-induced fluorescent selective upper tract urinary cytology.

OBJECTIVES: To investigate the efficacy of selective upper tract urinary cytology using extracorporeal 5-aminolevulinic acid for the diagnosis of upper urinary tract urothelial carcinoma. METHODS: We evaluated 104 patients who underwent radical nephroureterectomy and were diagnosed pathologically as having upper urinary tract urothelial carcinoma between March 2013 and May 2019 in Osaka Rosai Hospital. Preoperatively, we collected upper tract urinary cytology from both sides, and compared the sensitivity and specificity between conventional urine cytology and 5-aminolevulinic acid-induced fluorescent urine cytology. RESULTS: The sensitivity of 5-aminolevulinic acid-induced fluorescent selective upper tract urinary cytology was significantly higher than conventional cytology (90.4% vs 66.3%, P < 0.001), whereas the specificity was equally high (100% vs 98.2%, P = 1.0). In more detailed analysis, the sensitivity of 5-aminolevulinic acid-induced fluorescent selective upper tract urinary cytology was significantly higher than that of conventional cytology unrelated to patients' age (<76 years: 90.2% vs 68.6%, P = 0.013; ≥76 years: 90.6% vs 64.2%, P = 0.021), sex (male: 89.2% vs 67.5%, P = 0.001; female: 95.2% vs 61.9%, P = 0.02) or pT stage (pT1 or less: 91.4% vs 69.0%, P = 0.005; pT2 or more: 89.1% vs 63.0%, P = 0.006), tumor grade (high grade: 91.0% vs 70.5%, P = 0.002; low grade: 88.5% vs 53.8%, P = 0.013), and tended to be more efficacious for tumors that could not be detected by imaging techniques (83.3% vs 50.0%, P = 0.075). CONCLUSIONS: 5-Aminolevulinic acid-induced fluorescent selective upper tract urinary cytology is more sensitive than conventional cytology for the diagnosis of upper urinary tract urothelial carcinoma, regardless of pT stage and tumor grade.

[Usefulness of Fluorescent Urine Cytology in the Diagnosis of Urothelial Carcinoma].

Five-aminolevulinic acid, an amino acid that is metabolized in the cytoplasm to become protoporphyrin IX, is used in photodynamic diagnosis in various carcinomas because it accumulates in higher concentrations in tumor tissue than in normal tissue. 5-Aminolevulinic acid-induced fluorescent urine cytology is more sensitive than conventional urine cytology only in low grade urothelial carcinoma (UC), but it showed a tendency for higher sensitivity in high grade UC. To increase the number of patients and reconsider our previous findings, we compared the sensitivity and specificity of preoperative urine cytology and fluorescent urine cytology in 343 patients diagnosed as having UCs pathologically (215 bladder cancers, 128 upper tract UCs) and 197 non-cancer patients at Osaka Rosai Hospital from March 2013 to December 2019. The sensitivities of fluorescent urine cytology and conventional urine cytology were 81.1% and 63.3% (p<0.001), respectively, and specificities were 92.9% and 93.9% (p=0.84), respectively. The sensitivity of fluorescent urine cytology was superior to that of conventional urine cytology in both low grade UC (76.8% vs 41.1%, p<0.001) and high grade UC (83.1% vs 74.0%, p=0.023).

[Late Recurrence of Seminoma Diagnosed by Endoscopic Ultrasound-Guided Fine Needle Aspiration in a Retroperitoneal Lymph Node].

The patient was a 43-year-old man. At 30 years of age, he underwent high-inguinal orchiectomy for a right testicular tumor and was diagnosed with seminoma pT1N0M0. The patient had been followed without additional treatment and had dropped out 7 years after surgery. At 43 years of age, abdominal ultrasonography performed for screening revealed a swollen 4 cm-wide intra-abdominal lymph node, and he was referred to our department. Abdominal contrast-enhanced computed tomography (CT) showed a mass with a 5 cm-wide contrast effect that contacted the anterior surface of the inferior vena cava from the duodenum to the aortic bifurcation. Histological examination by trans-duodenal ultrasound-guided fineneedle aspiration suggested late recurrence of seminoma. After receiving three courses of BEP (bleomycin, etoposide, and platinum) therapy, the patient underwent laparoscopic lymphadenectomy. Pathological examination showed no residual tumor, and the patient was free of recurrence at 13 months after surgery.

High diagnostic efficacy of 5-aminolevulinic acid-induced fluorescent urine cytology for urothelial carcinoma.

BACKGROUND: In general, urine cytology is often problematic because of its low sensitivity, especially for low-grade urothelial carcinoma (UC) in clinical practice. To improve the sensitivity, we focused on 5-aminolevulinic acid (5-ALA), because recent studies suggested that 5-ALA-induced urine cytology can be used for photodynamic diagnosis. In this study, we evaluated the diagnostic efficacy of 5-ALA-induced fluorescent urine cytology for UC. METHODS: We included in this study 318 patients comprising 158 non-cancer patients, 84 bladder tumor patients, and 76 upper urinary tract urothelial carcinoma (UUT-UC) patients treated in our institution from March 2013 to September 2018. Using the same voided urine sample, we compared sensitivity and specificity between conventional urine cytology and 5-ALA-induced fluorescent urine cytology. RESULTS: Overall, the sensitivity of 5-ALA-induced fluorescent urine cytology was significantly higher than that of conventional urine cytology (86.9% vs. 69.4%; p = 0.0002), and the specificity was equivalently high (96.2% vs. 95.6%; p = 1.0). In subgroup analysis, the high sensitivity of 5-ALA-induced fluorescent urine cytology was also detected regardless of age, sex, and tumor type. However, in terms of stage and grade, differences were only detected in patients with less than pTa stage (89.2% vs. 52.1%; p = 0.0001) and low-grade tumor (91.5% vs. 51.1%; p < 0.0001). CONCLUSIONS: 5-ALA-induced fluorescent urine cytology was significantly more effective for UC diagnosis when compared with the conventional cytology, especially in patients with low-stage and low-grade tumors. These findings indicate that 5-ALA-induced fluorescent urine cytology may potentially be a very useful tool for clinical use.

Extracellular vesicles isolated from human renal cell carcinoma tissues disrupt vascular endothelial cell morphology via azurocidin.

Cancer-associated extracellular vesicles (EVs) are intimately involved in establishment of tumor microenvironment and occurrence of metastasis. However, previous studies have mainly relied on experiments with cultured cell lines or mouse models, making it difficult to gain a full understanding of EV functions in human body. Hence, we extracted EVs directly from surgically resected viable clear cell renal cell carcinoma (ccRCC) tissues and adjacent normal renal tissues (n = 20). Quantitative LC/MS analysis identified 3,871 tissue-exudative EV (Te-EV) proteins, among which azurocidin (AZU1) was highly enriched in tumor Te-EVs (p = 2.85 × 10-3 , fold-change = 31.59). Importantly, AZU1 content was also significantly higher in serum EVs from ccRCC patients compared to those from healthy donors. We further found that ccRCC-derived EVs had AZU1-dependent membrane permeabilizing activity for the vascular endothelial cell layer. Thus Te-EVs should be ideal resource for investigation of physiological EV functions.

[Renal Pelvic Cancer with Delayed Diagnosis Due to Left Renal Injury : A Case Report].

We report a case of renal pelvic cancer found after left renal trauma. A 63-year-old man was admitted to our hospital because of gross hematuria after he had fallen down the stairs two days earlier. He had asymptomatic severe anemia (Hb : 3. 6 g/dl). Abdominal computed tomography (CT) scan revealed bilateral ureteropelvic stones, bilateral severe hydronephrosis and hematoma of the left upper renal pelvis. We diagnosed him with left renal pelvic hemorrhage by trauma, and transcatheter arterial embolization (TAE) was performed. After TAE, gross hematuria improved, but some hematuria continued to be noted. We suspected malignancy, and examined the patient with contrast-enhanced CT, transurethral resection and retrograde pyelography combined with urine cytology in the upper urinary tract, all with no evidence of malignancy. However, four months after the left renal injury, follow-up CT revealed multiple metastatic lesions. We performed a left nephrectomy, and the resulting pathological diagnosis was invasive urothelial carcinoma with squamous differentiation of the renal pelvis. We performed 7 courses of chemotherapy, but the multiple metastatic lesions progressed, and he died of the disease 19 months after the operation.

Expression level of CXCL7 in peripheral blood cells is a potential biomarker for the diagnosis of renal cell carcinoma.

There are no blood biomarkers for the diagnosis of renal cell carcinoma (RCC) in routine clinical use. We focused on the gene expression profile of peripheral blood cells obtained from RCC patients to discover novel biomarkers for RCC diagnosis. Using microarray analysis and quantitative verification, CXCL7 was shown to be significantly upregulated in the peripheral blood cells of RCC patients. Importantly, aberrant CXCL7 expression was confirmed even in peripheral blood cells obtained from early stage (pT1a) RCC patients, and the expression level of CXCL7 in peripheral blood cells was a potential independent biomarker for the diagnosis of RCC by receiver operating characteristic curve analysis (sensitivity, 70.0%; specificity, 64.0%; area under the curve = 0.722; multiple logistic regression analysis: odds ratio, 1.07; 95% confidence interval, 1.03-1.11; P = 0.0004). Moreover, CXCL7 expression in peripheral blood cells significantly decreased after resection of the primary tumor. CXCL7 is more highly expressed in PBMCs than in neutrophils from both healthy controls and RCC patients. Interestingly, CXCL7 expression in PBMCs from healthy volunteers was significantly elevated following coculture with RCC cells compared to those cocultured with normal cells as a control. These results suggest that aberrant CXCL7 expression in peripheral blood cells is induced by RCC cells and may serve as a novel biomarker in the diagnosis of RCC.

[A Case of Retroperitoneal Mature Teratoma with Combined Resection of Left Kidney].

A 37-year-old woman with the complaint of stomachache was referred to our hospital because a retroperitoneal tumor was detected in an ultrasound study at another hospital. Magnetic resonance imaging showed a poorly enhanced 14 cm tumor in the left retroperitoneal space suggesting a cyst that contained fat and showed calcification. Abdominal dynamic computed tomography revealed left renal vein stenosis and left ovarian vein dilation caused by tumor compression of the renal vein. The tumor was excised together with the left kidney because the renal vein was adhered to the tumor. The resected specimen weighed 1,300 g, and the histological diagnosis was mature teratoma. The patient has experienced no recurrence at eight months after surgery.

Bone marrow-derived cells contribute to regeneration of injured prostate epithelium and stroma.

BACKGROUND: Recent studies have reported that bone marrow-derived cells (BMDCs), which are recruited to sites of tissue injury and inflammation, can differentiate into epithelial cells, such as liver, lung, gastrointestinal tract, and skin cells. We investigated the role of BMDCs in contributing to regeneration of injured prostate epithelium. METHODS: Using chimera rats that received allogenic bone marrow grafts from green fluorescent protein (GFP) transgenic rats after lethal whole-body irradiation, we investigated the existence of epithelial marker-positive BMDCs in injured prostate tissue caused by transurethral injection of lipopolysaccharide. RESULTS: Prostate tissues were harvested 2 weeks after transurethral lipopolysaccharide injection. Immunofluorescence staining showed that some cells in the stroma co-expressed GFP and pan-cytokeratin, which suggested the existence of epithelial marker-positive BMDCs. To confirm the existence of such cells, we collected bone marrow-derived non-hematopoietic cells (GFP+/CD45- cells) from the prostate by fluorescence-activated cell sorter analysis and analyzed the characteristics of the GFP+/CD45- cells. The number of cells in this population significantly increased from 0.042% to 0.492% compared with normal prostate tissue. We found by immunofluorescent analysis and RT-PCR that GFP+/CD45- cells expressed cytokeratin, which suggested that these cells have some features of epithelial cells. In the prostate obtained from the chimera rats 34 weeks after lipopolysaccharide injection, GFP- and cytokeratin-positive cells were observed in the prostate gland, which suggested that some of the cells in the prostate gland regenerated after prostate inflammation derived from bone marrow. CONCLUSIONS: BMDCs might be able to differentiate into prostate epithelial cells after prostatic injury.

Preoperative risk stratification for cancer-specific survival of patients with upper urinary tract urothelial carcinoma treated by nephroureterectomy.

BACKGROUND: This study aimed to identify preoperative parameters for predicting cancer-specific survival (CSS) in patients with upper urinary tract urothelial carcinoma (UTUC) who have undergone radical nephroureterectomy (RNU). METHODS: The preoperative clinical and laboratory records of 357 UTUC patients who underwent RNU at three different institutions were retrospectively reviewed (256, training set; 101, test set). Univariate and multivariate analyses were performed on the training set data to identify preoperative prognostic factors, using which a risk stratification model was developed. The model was validated using test set data. RESULTS: In univariate analysis, clinical T stage classification and preoperative concentrations of hemoglobin, C-reactive protein, sodium, and albumin showed significant association with CSS. Multivariate analysis showed that low preoperative sodium and hemoglobin concentrations were significantly associated with a poor prognosis. A risk stratification model was developed using the preoperative sodium (<141 mEq/L) and hemoglobin concentrations (below normal). Three subgroups were formed depending on the presence of no (favorable group), one (intermediate), or two (poor) prognostic factors, and the 5-year CSS estimates were found to be 96.5, 75.5, and 47.0 %, respectively (P < 0.01). The risk model was significantly associated with the adverse pathological findings of stage pT3 or more and lymphovascular invasion (P = 0.005). CONCLUSION: We identified low preoperative sodium and hemoglobin concentrations as prognostic factors for patients with UTUC treated with RNU. Our risk stratification model may help physicians design a therapeutic strategy.

Serum fucosylated haptoglobin as a novel prognostic biomarker predicting high-Gleason prostate cancer.

BACKGROUND: Fucosylation is an oligosaccharide modification associated with cancer and inflammation, which is catalyzed by fucosyltransferases. Fucosylated haptoglobin (Fuc-Hpt) has been identified as a novel biomarker for pancreatic cancer. In this study, we evaluated serum Fuc-Hpt as a biomarker for prostate cancer, and investigated the expression of fucosyltransferases and haptoglobin in prostate cancer cell lines. METHODS: We measured the preoperative serum Fuc-Hpt levels in 98 patients who underwent radical prostatectomy (RP) using an established lectin-antibody ELISA. Fucosyltransferase and haptoglobin mRNA and protein expressions in prostate cancer cell lines were determined using quantitative PCR and Western blotting. RESULTS: Serum Fuc-Hpt levels were significantly associated with Gleason score (GS), but not prostate-specific antigen (PSA) levels. The area under the receiver-operator characteristics curve (AUC) for the prediction of GS ≥7 in prostatectomy specimens by Fuc-Hpt was 0.753, in contrast to the PSA AUC of 0.561 and the PSAD AUC of 0.558. The Fuc-Hpt AUC for the prediction of GS upgrade from GS 6 at biopsy to GS ≥7 after RP was 0.689, in contrast to the PSA AUC of 0.588 and PSAD AUC of 0.557. Multivariable analysis revealed that Fuc-Hpt levels were significantly associated with biochemical recurrence after prostatectomy. A high expression of alpha-(1-6) fucosyltransferase (FUT8) and haptoglobin was observed in prostate cancer cell line, suggesting that certain kinds of prostate cancer cells produce Fuc-Hpt. CONCLUSION: Elevated serum Fuc-Hpt level could be a novel cancer biomarker for predicting the prognosis of patients with prostate cancer, particularly those with high GSs.

Microvessel area of immature vessels is a prognostic factor in renal cell carcinoma.

OBJECTIVES: To analyze the presence of immature vessels as a predictive factor of prognosis in patients with renal cell carcinoma. METHODS: Tissue samples were obtained from 50 renal cell carcinoma patients who underwent radical nephrectomy, and the blood vessels were stained using antibodies to cluster of differentiation 34 and α-smooth muscle actin. Immature vessels were defined as those positive for cluster of differentiation 34, and mature vessels as those positive for both cluster of differentiation 34 and α-smooth muscle actin. The extent of vascularization was quantified by calculating the microvessel area and microvessel density. RESULTS: The microvessel area of immature vessels was positively associated with tumor grade (P < 0.0001), T stage (P < 0.0001) and American Joint Committee on Cancer stage (P < 0.0001), and was significantly higher in tumors with metastasis than in those without metastasis (P < 0.0001). The microvessel density did not associate with tumor grade or T stage. The disease-free survival and overall survival were significantly shorter in patients with high microvessel area. CONCLUSIONS: The microvessel area of immature vessels seems to be associated with renal cell carcinoma aggressiveness, suggesting this might be considered as a novel prognostic factor in patients with these tumors.