Recent advances in the molecular genetics of urogenital tumors

Wnt-signaling and senescence: A tug of war in early neoplasia?

Studies of early neoplasia have revealed fundamental molecular pathways that drive tumorigenesis. Despite this progress, synthesis of principles of tumorigenesis that span tissue types has lagged. Such forays into the 'comparative anatomy' of cancer can stimulate new models and refine key questions. We envision commonality of pathways important in formation of two early benign neoplasms that are found in different tissues and which are not generally thought to be similar: dysplastic nevi of the skin and intestinal aberrant crypt foci. We propose that these neoplasms result from an ongoing 'tug of war' between the tumor suppression barrier posed by cellular senescence and the tumor-promoting activity of Wnt-signaling. Whether or not such neoplasms progress to malignancy or persist in a benign state for many years might be largely determined by the outcome of this tug of war and its modulation by other genetic and epigenetic alterations, such as inactivation of p16(INK4a).

Downregulation of Wnt signaling is a trigger for formation of facultative heterochromatin and onset of cell senescence in primary human cells

Cellular senescence is an irreversible proliferation arrest of primary cells and an important tumor suppression process. Senescence is often characterized by domains of facultative heterochromatin, called senescence-associated heterochromatin foci (SAHF), which repress expression of proliferation-promoting genes. Formation of SAHF is driven by a complex of histone chaperones, HIRA and ASF1a, and depends upon prior localization of HIRA to PML nuclear bodies. However, how the SAHF assembly pathway is activated in senescent cells is not known. Here we show that expression of the canonical Wnt2 ligand and downstream canonical Wnt signals are repressed in senescent human cells. Repression of Wnt2 occurs early in senescence and independently of the pRB and p53 tumor suppressor proteins and drives relocalization of HIRA to PML bodies, formation of SAHF and senescence, likely through GSK3beta-mediated phosphorylation of HIRA. These results have major implications for our understanding of both Wnt signaling and senescence in tissue homeostasis and cancer progression.

Predicting disease outcome of non-invasive transitional cell carcinoma of the urinary bladder using an artificial neural network model: results of patient follow-up for 15 years or longer

BACKGROUND

Patients with non-invasive (Ta/T1) transitional cell carcinoma (TCC) of the urinary bladder are often observed without progression in the long-term follow-up period, although many of them experience recurrence of disease. It is difficult to accurately predict the disease outcome of each patient with Ta/T1 TCC using conventional prognostic criteria. In this study, we examined the usefulness of artificial neural networks (ANNs) to predict the long-term disease outcome of patients with TCC of the urinary bladder.

METHODS

A retrospective, prognostic study of 90 patients with Ta/T1 TCC of the urinary bladder, diagnosed by transurethral resection of the bladder tumor between April 1981 and March 1985, and then followed up for 15 years or longer, was carried out. Data were analyzed using the Bayesian network tool of SPSS Neural Connection 2.1. The input neural data consisted of tumor stage, grade, tumor number, age, gender, tumor architecture and estimates of mean nuclear volume. The data set was randomly divided into 68 training and 22 testing examples for the prediction of disease progression and tumor recurrence within 15 years.

RESULTS

During 15 years follow-up, tumor recurrence was noted in 42/90 (47%) Ta/T1 tumors. The ANN model could not predict tumor recurrence. Conversely, disease progression was noted in 17/90 (19%) Ta/T1 tumors, and, in the test set, 4/22 (18%) Ta/T1 tumors underwent disease progression. The sensitivity of the ANN model to predict progression was 100% (specificity 67%; positive predictive value 40%; negative predictive value 100%). Patients who were judged to have a favorable prognosis using ANN analysis did not progress within the 15-year follow-up period.

CONCLUSION

The results of the ANN study indicate that long-term progression-free survival of patients with non-invasive TCC of the urinary bladder can be precisely predicted. A favorable prognosis using ANNs would be one of the exclusion criteria for immediate or future total cystectomy.

Distinct patterns of chromosomal losses in clinically synchronous and asynchronous bilateral renal cell carcinoma

PURPOSE

Bilateral renal cell carcinoma has been reported to occur in 1% to 4% of patients with renal cancer. However, whether bilateral renal cell carcinoma involves metastatic lesions of the contralateral kidney or develops as simultaneous primary tumors remains unclear to date. Thus, we investigated chromosomal losses and von Hippel-Lindau (VHL) gene abnormalities in bilateral tumors from patients with nonfamilial bilateral renal cell carcinoma.

MATERIALS AND METHODS

Genomic DNA was exacted from 2 tumors in 8 patients each with nonfamilial bilateral renal cell carcinoma, including clinically asynchronous and synchronous disease in 5 and 3, respectively. The DNA was then subjected to microsatellite analysis on 13 chromosomal loci. In addition, polymerase chain reaction-single nucleotide specific conformation polymorphism analysis and direct sequencing of 3 exons of the VHL gene were performed.

RESULTS

All 5 asynchronous cases showed loss of the same allele in bilateral tumors, indicating a common clonal origin. In contrast, 2 of the 3 synchronous cases showed different patterns of chromosomal loss in the right and left renal tumors, suggesting bilateral primary origins. The other synchronous case with loss of the same allele in each tumor involved right stage T3b and left stage T1a neoplasms. No VHL gene mutations were detected in any case.

CONCLUSIONS

Except for a small number of cases synchronous and asynchronous bilateral renal cell carcinoma may represent the simultaneous appearance of separate primary tumors and metastatic progression from the contralateral kidney, respectively.

Allelic imbalances on chromosome 20 in human transitional cell carcinoma

One determinant of the survival time of cancer-bearing patients may be genetic factors. In chemically induced bladder cancers of mice, differences in survival time have been observed among several inbred strains. Genetic analyses of such differences in crosses between C57BL / 6 and NON mice revealed that the survival period is determined by two quantitative trait loci on mouse chromosomes 6 and 2, respectively. We explored the possibility that genetic alterations may be observed in the syntenic conserved chromosomal regions of human transitional cell carcinoma corresponding to mouse chromosomes 6 and 2. Human chromosome 7, containing a region syntenic to mouse chromosome 6, is reported to harbor frequent genetic alterations in bladder cancers. In this study, we investigated 70 human urothelial cancers for possible genetic alterations on human chromosome 20p and 20q containing regions syntenic to mouse chromosome 2. Allelic imbalances were observed in 22 cases (31.4%) on 20p and 18 cases (25.7%) on 20q. Those allelic imbalances, however, did not show a direct correlation with the prognosis of the patients. Higher grade tumors tended to show more frequent imbalances on chromosome 20; however, this tendency was not significant.