Role of the retinoblastoma gene in the initiation and progression of human cancer

RB1 5́UTR contains an IRES related to cell cycle control and cancer progression

Retinoblastoma gene1 (RB1) is the first tumor suppressor gene that stands as the guardian of the gate of the G1 period and plays a central role in proliferation and differentiation. However, no reports focused on the possible internal ribosome entry site (IRES) function of the RB1 gene flanking sequence. In this study, we constructed a bicistronic reporter with the RB1 5'untranslated region (5́UTR) inserted between two reporter coding regions. We found RB1 5'UTR harbors an IRES and has higher activity in cancer cell lines than normal cells. Besides, RB1 IRES acquired the highest activity in the G0/G1 phase of the cell cycle, and the RB1 5'UTR mutation collected from retinoblastoma decreased IRES activity compared with RB1 5'UTR wild-type. These data indicated that RB1 IRES is a mechanism of stress regulation and is related to cell cycle control and cancer progression.

Using a Novel Diagnostic Nomogram to Differentiate Malignant from Benign Parathyroid Neoplasms

We sought to develop an immunohistochemical (IHC) tool to support the diagnosis of parathyroid carcinoma (PC) and help differentiate it from atypical parathyroid neoplasms (atypical) and benign adenomas. Distinguishing PC from benign parathyroid neoplasms can be challenging. Many cases of PC are histopathologically borderline for definitive malignancy. Recently, individual IHC biomarkers have been evaluated to aid in discrimination between parathyroid neoplasms. PC, atypical parathyroid neoplasms, and parathyroid adenomas treated at our institution from 1997 to 2014 were studied retrospectively. IHC analysis was performed to evaluate parafibromin, retinoblastoma (RB), protein gene product 9.5 (PGP9.5), Ki67, galectin-3, and E-cadherin expression. Receiver operating characteristic (ROC) analysis and multivariable logistic regression model for combinations of biomarkers were evaluated to classify patients as PC or atypical/adenoma. A diagnostic nomogram using 5 biomarkers was created for PC. Sixty-three patients were evaluated. The percent staining of parafibromin (p < 0.0001), RB (p = 0.04), Ki67 (p = 0.02), PGP9.5 (p = 0.04), and Galectin-3 (p = 0.01) differed significantly in the three diagnostic groups. ROC analysis demonstrated that parafibromin had the best performance in discriminating PC from atypical/adenoma; area under the curve (AUC) was 81% (cutoff, 92.5%; sensitivity rate, 64%; specificity rate, 87%). We created a diagnostic nomogram using a combination of biomarkers; AUC was 84.9% (95% confidence interval, 73.4-96.4%). The optimism-adjusted AUC for this model was 80.5% (mean absolute error, 0.043). A diagnostic nomogram utilizing an immunoexpression, a combination of immunohistochemical biomarkers, can be used to help differentiate PC from other parathyroid neoplasms, thus potentially improving diagnostic classification.

Expression Analysis of RbBP6 in human cancers: a Prospective biomarker

Retinoblastoma binding protein 6 (RBBP6) is a cancer-related protein that has been implicated in the regulation of cell cycle and apoptosis. RBBP6 isoform 1 has been demonstrated to interact with two tumour suppressors, p53 and pRB. Isoform 1 been shown to regulate p53 through its ubiquitin ligase activity, thus implicating in cell cycle regulation and apoptosis. Isoforms 1 and 2 are multidomain proteins containing a domain with no name (DWNN) domain, a Zinc Finger, a RING Finger, an Rb-binding domain and a p53-binding domain. The RBBP6 isoform 3 comprises the DWNN domain only. Isoform 4 lacks the Rb-binding domain but its role is less understood. RBBP6 isoform 3 has been reported as a cell cycle regulator with anticancer potential. There have been several studies that have clearly demonstrated that RBBP6 may be an important biomarker for cancer diagnosis and a potential drug target for cancer treatment. This work focused on differential expression of RBBP6 transcripts in different cancers, providing detailed analysis of their potential as diagnostic biomarkers for different cancers. These cancers include breast, liver, cervical and colon carcinomas. The expression of RBBP6 transcripts may further provide better understanding of the role of the RBBP6 in carcinogenesis and cell homeostasis.

A rare combination consisting of aldosterone-producing adenoma and adrenal myelolipoma in a patient with heterozygosity for retinoblastoma (RB) gene

Various pathological disorders have been associated with primary aldosteronism, including glucagonoma, phaeochromocytoma and primary hyperparathyroidism.

In this report, a case of adrenal myelolipoma (a rare non-functioning tumour composed of mature adipose tissue and normal haematopoietic elements similar to bone marrow cells), aldosterone-producing adenoma and a pituitary microadenoma coexisting in a 62-year-old man with a 15-year history of arterial hypertension, previous ablation of an autonomously-functioning thyroid adenoma, multiple lipomas and an heterozygosity of the retinoblastoma (RB) susceptibility gene is reported.

We believe that this case probably represents another variant of the multiple neoplasia syndrome and we speculate that structural alteration of the RB gene may play a role in the tumorogenesis.

Paediatric retinoblastoma in India: evidence from the National Cancer Registry Programme

BACKGROUND

Globally, retinoblastoma is the most common primary intraocular malignancy occurring in children. This paper documents the recent incidence rates of retinoblastoma by age and sex groups from the Population Based Cancer Registries (PBCRs) of Bangalore, Mumbai, Chennai, Delhi and Kolkata using the data from the National Cancer Registry Programme.

MATERIALS AND METHODS

Relative proportions, sex ratio, method of diagnosis, and incidence rates (crude and age standardized) for each PBCR and pooled rates of the five PBCRs were calculated for the years 2005/06 to 2009/10. Standard errors and 95% confidence limits of ASIRs by sex group in each PBCR were calculated using the Poisson distribution. Standardised rate ratios of ASIR by sex group and rate ratios at risk were also calculated.

RESULTS

The maximum retinoblastoma cases were in the 0-4 age group, accounting for 78% (females) and 81% (males) of pooled cases from five PBCRs. The pooled crude incidence rate in the 0-14 age group was 3.5 and the pooled ASIR was 4.4 per million. The pooled ASIR in the 0-4, 5-9 and 10-14 age group were 9.6, 2.0 and 0.1 respectively. The M/F ratio in Chennai (1.9) and Bangalore PBCRs (2.0) was much higher than the other PBCRs. Among the PBCRs, the highest incidence rate in 0-4 age group was found in males in Chennai (21.7 per million), and females in Kolkata (18.9 per million). There was a distinct variation in incidence rates in the PBCRs in different geographic regions of India.

Reduced expression of the retinoblastoma protein shows that the related signaling pathway is essential for mediating the antineoplastic activity of erufosine

Erufosine is a new antineoplastic agent of the group of alkylphosphocholines, which interferes with signal transduction and induces apoptosis in various leukemic and tumor cell lines. The present study was designed to examine for the first time the mechanism of resistance to erufosine in malignant cells with permanently reduced expression of the retinoblastoma (Rb) protein. Bearing in mind the high number of malignancies with reduced level of this tumor-suppressor, this investigation was deemed important for using erufosine, alone or in combination, in patients with compromised RB1 gene expression. For this purpose, clones of the leukemic T-cell line SKW-3 were used, which had been engineered to constantly express differently low Rb levels. The alkylphosphocholine induced apoptosis, stimulated the expression of the cyclin dependent kinase inhibitor p27^Kip1 and inhibited the synthesis of cyclin D3, thereby causing a G₂ phase cell cycle arrest and death of cells with wild type Rb expression. In contrast, Rb-deficiency impeded the changes induced by eru-fosine in the expression of these proteins and abrogated the induction of G₂ arrest, which was correlated with reduced antiproliferative and anticlonogenic activities of the compound. In conclusion, analysis of our results showed for the first time that the Rb signaling pathway is essential for mediating the antineoplastic activity of erufosine and its efficacy in patients with malignant diseases may be predicted by determining the Rb status.

Altered p16(INK4) and RB1 Expressions Are Associated with Poor Prognosis in Patients with Nonsmall Cell Lung Cancer

p16(INK4) and RB1 are two potent cell cycle regulators to control the G1/S transition by interacting with CDK4/6, E2F, and D-type cyclins, respectively. Depending on the tumour type, genetic alterations resulting in the functional inactivation have frequently been reported in both genes. By contrast, much less is known regarding the overexpression of these proteins in the tumor cells. In this study, expressions of p16(INK4) RB1, and CDKN2A copy number variances (CNV) in the tumor cells were assessed by immunohistochemistry and fluorescence in situ hybridization (FISH), respectively, in 73 nonsmall cell lung cancer (NSCLC) with known 5-year survivals. The histologic type (P = 0.01), p16(INK4) (P = 0.004), and RB1 (P < 0.001) were predictive of survivals. The CDKN2A CNV (P < 0.05) was also significant when compared to those cases without CNV. Therefore, among the molecular genetic prognostic factors, expressions of RB1 and p16(INK4) in the tumor cells were the most strongly predictive of adverse outcomes in stage I and II nonsquamous NSCLC.

Thinking about repairing thinking

The work of Sinden et al. suggests that it may be possible to produce improvement in the “highest” areas of brain function by transplanting brain tissue. What appears to be the limiting factor is not the complexity of the mental process under consideration but the discreteness of the lesion which causes the impairment and the appropriateness and accuracy of placement of the grafted tissue.

Therapeutic uses for neural grafts: Progress slowed but not abandoned

In spite of Stein and Glasier's justifiable conclusion that initial optimism concerning the immediate clinical applicability of neural transplantation was premature, there exists much experimental evidence to support the potential for incorporating this procedure into a therapeutic arsenal in the future. To realize this potential will require continued evolution of our knowledge at multiple levels of the clinical and basic neurosciences.

The structure, operation, and functionality of intracerebral grafts

The concept of structure, operation, and functionality, as they may be understood by clinicians or researchers using neural transplantation techniques, are briefly defined. Following Stein & Glasier, we emphasize that the question of whether an intracerebral graft is really functional should be addressed not only in terms of what such a graft does in a given brain structure, but also in terms of what it does at the level of the organism.

The NGF superfamily of neurotrophins: Potential treatment for Alzheimer's and Parkinson's disease

Stein & Glasier suggest embryonic neural tissue grafts as a potential treatment strategy for Alzheimer's and Parkinson's disease. As an alternative, we suggest that the family of nerve growth factor-related neurotrophins and their trk (tyrosine kinase) receptors underlie cholinergic basal forebrain (CBF) and dopaminergic substantia nigra neuron degeneration in these diseases, respectively. Therefore, treatment approaches for these disorders could utilize neurotrophins.

Some practical and theoretical issues concerning fetal brain tissue grafts as therapy for brain dysfunctions

Grafts of embryonic neural tissue into the brains of adult patients are currently being used to treat Parkinson's disease and are under serious consideration as therapy for a variety of other degenerative and traumatic disorders. This target article evaluates the use of transplants to promote recovery from brain injury and highlights the kinds of questions and problems that must be addressed before this form of therapy is routinely applied. It has been argued that neural transplantation can promote functional recovery through the replacement of damaged nerve cells, the reestablishment of specific nerve pathways lost as a result of injury, the release of specific neurotransmitters, or the production of factors that promote neuronal growth. The latter two mechanisms, which need not rely on anatomical connections to the host brain, are open to examination for nonsurgical, less intrusive therapeutic use. Certain subjective judgments used to select patients who will receive grafts and in assessment of the outcome of graft therapy make it difficult to evaluate the procedure. In addition, little long-term assessment of transplant efficacy and effect has been done in nonhuman primates. Carefully controlled human studies, with multiple testing paradigms, are also needed to establish the efficacy of transplant therapy.

Models of neurological defects and defects in neurological models

The transition from research to patient following advances in transplantation research is likely to be disappointing unless it includes a better understanding of critically relevant characteristics of the neurological disorder and improvements in the animal models, particularly the behavioral features. The appropriateness of the model has less to do with the species than with how the species is used.

Predicting survival after radical cystectomy for bladder cancer

Accurate prediction is essential for patient counselling, appropriate selection of treatments and determination of eligibility for clinical trials. In this review we assess the available determinants of oncological outcome after radical cystectomy (RC) for transitional cell carcinoma of the urinary bladder. We reviewed previous publications to provide guidelines in terms of criteria, limitations and clinical value of available tools for predicting patient outcome after RC. Our findings suggest that while individual surgical, patient and pathological features provide useful estimates of survival outcome, the inherent heterogeneity of tumour biology and patient characteristics leads to significant variation in outcome. By incorporating all relevant continuous predictive factors for individual patients, integrative predictive models, such as nomograms or artificial neural networks, provide more accurate predictions and generally surpass clinical experts at predicting outcomes. Nonetheless, there is a clear need for the development and validation of molecular biomarkers and their incorporation into multivariable predictive tools. Significant progress has been made in identifying important molecular markers of disease and the development of multifactorial tools for predicting the outcome after RC.

Promoter hypermethylation profile of cell cycle regulator genes in pituitary adenomas

Aberrant hypermethylation of CpG islands in the promoter region plays a causal role in the inactivation of various key genes involved in the cell cycle regulatory cascade, which could result in a loss of cell cycle control. The aim of the present study was to examine in more detail the prevalence and role of the promoter methylation of genes with a proven involvement in the cell cycle regulation of pituitary adenomas, since their tumorigenesis has not yet been clearly defined. We profiled the CpG island methylation status of a series of well-characterized cell cycle regulation genes: the RB1, p14(ARF), p15(INK4b), p16(INK4a), p21(Waf1/Cip1), p27(Kip1), and p73 genes, in 34 pituitary adenomas as determined by a methylation-specific polymerase chain reaction assay. Promoter hypermethylation of the RB1, p14(ARF), p15(INK4b), p16(INK4a), p21(Waf1/Cip1), p27(Kip1), and p73 genes was detected in 12 (35%), 2 (6%), 11 (32%), 20 (59%), 1 (3%), 0 (0%), and 4 (12%) of the adenomas, respectively. In total, 88% (30 of 34) of the adenomas displayed methylation of at least one of such cell cycle regulatory genes, especially methylation of the member genes of the RB1 pathway (29 of 34; 85%). Promoter hypermethylation of p15(INK4b) coincided with RB1 and/or p16(INK4a) methylation, whereas RB1 and p16(INK4a) methylations tended to be mutually exclusive (p = 0.0048). Furthermore, promoter hypermethylations of p14(ARF), p21(Waf1/Cip1), and p73 (not belonging to the member genes of the RB1 pathway) were also coincident with RB1 and/or p16(INK4a) methylation except in one p73 methylated case. In contrast, none of the clinicopathological features, including the cell proliferation index, was significantly correlated with any particular methylation status. Our results suggested that aberrant hypermethylation of the key cell cycle regulatory genes occurs at a relatively high frequency in pituitary adenomas, especially in RB1 pathway genes with promoter hypermethylation of the p16(INK4a) gene being the most common deregulation. We further obtained evidence to indicate that RB1 and p16(INK4a) methylations tended to be mutually exclusive, but did occasionally coincide with other cell cycle regulation gene methylations.

Expression of altered retinoblastoma protein inversely correlates with tumor invasion in gastric carcinoma

AIM: To investigate the clinical and pathological significance of altered retinoblastoma (Rb) encoding protein (pRb) in gastric carcinoma.

METHODS: Expression of altered pRb was analyzed in 91 patients with gastric adenocarcinoma by immunohistochemistry.

RESULTS: Sixty-five percent (59/91) of the tumors were positively stained and the staining in tumor nuclei of gastric carcinoma ranged 0%-90%. Moreover, strong expression of altered pRb was found in 35% (6/17), 24% (5/21), 17% (8/46) and 0% (0/7) of T1, T2, T3 and T4 gastric carcinomas, respectively. Altered pRb expression was inversely correlated with the depth of tumor invasion (P = 0.047). Degree of immunoreactivity had no significant correlation with tumor grade, node metastasis and distant metastasis. In terms of prognostic significance, univariate analysis showed that poor differentiation [41 (66.1%) vs 34 (42.5%) P = 0.051], advanced tumor stage (P < 0.001) and weakly altered pRb expression [17 (80.5%) vs 58 (49.6%) P = 0.044] were associated with worse prognosis in these patients. However, multivariate analysis revealed that advanced tumor stage was the only independent poor prognostic factor (P < 0.001).

CONCLUSION: The mutation of Rb gene is frequent in gastric carcinoma. The expression of altered pRb inversely correlates with tumor invasion and is not an independent prognostic marker in gastric adenocarcinoma.

The p15(INK4b)/p16(INK4a)/RB1 pathway is frequently deregulated in human pituitary adenomas

Pituitary adenomas are common benign intracranial neoplasms. However, their tumorigenesis is not yet clearly defined. Inactivation of genes involved in the negative cell-cycle regulatory p15(INK4b) - p16(INK4a) -cyclin D/CDK4-RB1-mediated pathway (RB1 pathway) is one of the most common and important mechanisms in the growth advantage of tumor cells. Recently, much attention has been focused on the importance of alternative mechanisms of gene inactivation, particularly promoter hypermethylation in the transcriptional silencing of such tumor-suppressor genes. Based on the rare occurrence of inactivation by gene mutations and deletions of the RB1 pathway in pituitary adenomas, we investigated the deregulation of the RB1 pathway in 42 sporadic human pituitary adenomas, especially focusing on the methylation status of this pathway as determined by a methylation-specific polymerase chain reaction assay. Homozygous deletion of the p15(INK4b) or p16(INK4a) gene was detected in one adenoma each. Amplification of the CDK4 gene was not apparent in any of the pituitary adenomas presently examined. Promoter hypermethylation of the p15(INK4b), p16(INK4a), and RB1 genes was detected in 15 (35.7%), 30 (71.4%), and 12 (28.6%) of the adenomas, respectively. Promoter hypermethylation of the p15(INK4b) gene coincided with p16(INK4a) alteration and/or RB1 methylation, whereas p16(INK4a) and RB1 methylations tended to be mutually exclusive (p = 0.019). Thus, the vast majority of the adenomas (38 of 42, 90.5%) displayed alterations of the RB1 pathway. None of the clinicopathologic features, including the proliferation cell index, was significantly correlated with any particular methylation status. Our results suggest that inactivation of the RB1 pathway may play a causal role in pituitary tumorigenesis, with hypermethylation of the p16(INK4a) gene being the most common deregulation, and further provide evidence that RB1 and p16(INK4a) methylations tend to be mutually exclusive but occasionally coincide with p15(INK4b) methylation.

Stratification of the biologic aggressiveness of non-small cell lung cancer using DNA flow cytometry and immunohistochemistry for the retinoblastoma protein

DNA ploidy pattern and S-phase fraction (SPF) measured by flow cytometry and expression of the retinoblastoma gene product (pRB) estimated by immunohistochemistry were correlated with outcome in 114 patients who received a curative operation for primary non-small cell lung cancer (NSCLC). One hundred ten tumors yielded an adequate DNA histogram, and all tumors exhibited an assessable immunohistochemical stain. DNA diploidy was detected in 31 tumors and DNA aneuploidy in 79 tumors. The mean SPF was 14.1 +/- 6.4%. Eighty tumors were positively stained, and 34 tumors were negative for pRB. Multivariate analysis clarified that both TNM staging and DNA ploidy were prognostic factors after surgery. In 39 recurrent cases, the SPF value was inversely correlated with disease-free interval. With only supportive care after recurrence, high SPF tumors and pRB-negative tumors progressed rapidly, whereas active treatment yielded an equivalent effect on recurrent tumors regardless of the SPF or pRB expression. DNA ploidy is related to the risk of recurrence, while SPF is related to tumor growth rate and the impact of active treatment on recurrence. The utility of pRB expression was limited. The combination of DNA ploidy and SPF allows practical stratification of the biologic aggressiveness of NSCLC.

Changes in retinoblastoma gene expression during cervical cancer progression

The role of tumour suppressor genes in the development of human cancers has been studied extensively. In viral carcinogenesis, the inactivation of suppressor proteins such as retinoblastoma (pRb) and p53, and cellular oncogenes overexpression, such as c-myc, has been the subject of a number of investigations. In uterine-cervix carcinomas, where high-risk human papillomavirus (HPV) plays an important role, pRb and p53 are inactivated by E7 and E6 viral oncoproteins, respectively. However, little is known about the in situ expression of some of these proteins in pre-malignant and malignant cervical tissues. On the other hand, it has also been demonstrated that c-myc is involved in cervical carcinogenesis, and that pRb participates in the control of c-myc gene expression. By using immunostaining techniques, we investigated pRb immunodetection pattern in normal tissues, squamous intraepithelial lesions (SILs) and invasive carcinomas from the uterine cervix. Our data show low pRb detection in both normal cervical tissue and invasive lesions, but a higher expression in SILs. C-Myc protein was observed in most of the cellular nuclei of the invasive lesions, while in SILs was low. These findings indicate a heterogeneous pRb immunostaining during the different stages of cervical carcinogenesis, and suggest that this staining pattern could be a common feature implicated in the pathogenesis of uterine-cervix carcinoma.

The APC tumor suppressor controls entry into S-phase through its ability to regulate the cyclin D/RB pathway

BACKGROUND & AIMS

APC gene mutation is an early alteration in most colorectal tumors. In an attempt to determine its role in tumor development, we asked whether reintroducing wild-type APC into colorectal cancer cells with mutant APC affected cell cycle progression.

METHODS

Using transient transfection, a plasmid containing the APC complementary DNA and DNA encoding the green fluorescent protein was expressed in SW480 cells. In addition, several other constructs were co-expressed with APC to determine their combined effects.

RESULTS

We report that colorectal cancer cell lines transfected with wild-type APC arrest in the G(1)- phase of the cell cycle and that this arrest is abrogated by cotransfecting constitutively active beta-catenin or cyclin D1 and cMYC together. This APC-induced cell cycle arrest involves the disruption of beta-catenin-mediated transcription and depends on components of the G(1)/S regulatory machinery, as overexpression of E1a or E2F-1, -2, or -3 overrides the G(1) arrest. Consistent with this, APC transfection inhibits RB phosphorylation and reduces levels of cyclin D1.

CONCLUSIONS

Our results suggest that APC functions upstream of RB in the G(1)/S regulatory pathway, cyclin D1 and cMYC affect APC-mediated arrest equivalently to oncogenic beta-catenin, and most colon tumors disrupt control of G(1)/S progression by APC mutation.

Role of tumor suppressor genes in the development of adult T cell leukemia/lymphoma (ATLL)

Adult T cell leukemia/lymphoma (ATLL) is one of the peripheral T cell malignant neoplasms strongly associated with human T cell leukemia virus type-I (HTLV-I). Although the viral transactivating protein Tax has been proposed to play a critical role in leukemogeneis as shown by its transforming activity in various experimental systems, additional cellular events are required for the development of ATLL. One of the genetic events in ATLL is inactivation of tumor suppressor genes. Among many candidates for tumor suppressor genes, the main genetic events have been reported to center around the cyclin-dependent kinase inhibitors ((CDKIs) p15INK4A, p16INK4B, p18INK4C, p19INK4D, p21WAF1, p27KIP1, and p57KIP2), p53 and Rb genes; all of them play a major regulatory role during G1 to S transition in the cell cycle. Acute/lymphomatous ATLL has frequent alterations of p15 (20%) and p16 (28-67%), while chronic/smoldering ATLL has fewer abnormalities of p15 (0-13%) and p16 (5-26%). Most of these changes are deletion of the genes; fewer samples have mutations. ATLL patients with deleted p15 and/or p16 genes have significantly shorter survival than those individuals with both genes preserved. Although genetic alterations of p18, p19, p21, p27 have rarely been reported, inactivation of these genes may contribute to the development of ATLL because low expression levels of these genes seem to mark ATLL. The p53 gene is mutated in 10-50% of acute/lymphomatous ATLL. Functional impairment of the p53 protein, even if the gene has wild-type sequences, has been suggested in HTLV-I infected cells. Each of these genetic events are mainly found in acute/lymphomatous ATLL, suggesting that alterations of these genes may be associated with transformation to an aggressive phenotype. The Rb tumor suppressor gene is infrequently structurally altered, but one half of ATLL cases have lost expression of this key protein. Notably, alterations of one of the CDKIs, p53 and Rb genes appear to obviate the need for inactivation of other genes in the same pathway. A novel tumor suppressor gene on chromosome 6q may also have a critical role in the pathogenesis of ATLL. Taken together, tumor suppressor genes are frequently altered in acute/lymphomatous ATLL and their alteration is probably the driving force fueling the transition from chronic/smoldering to acute/lymphomatous ATLL.

Cellular and molecular pathology of prostate cancer precursors

Prostate cancer is usually heterogeneous and multifocal, with diverse clinical and morphologic manifestations. Current understanding of the molecular basis for this heterogeneity is limited, particularly for prostatic intraepithelial neoplasia (PIN), the only putative precursor which can be identified according to morphologic criteria. However, it is likely that prostatic adenocarcinoma might arise from precursor lesions other than PIN, although these cannot be recognized with certainty at the present time. In this review, we summarize the current state of knowledge regarding the cell-biological and genetic bases for linking PIN and prostatic adenocarcinoma. It is conceivable that a stem cell of basal phenotype, or an amplifying cell, is the target of prostatic carcinogenesis. Prominent genetic heterogeneity is characteristic of both PIN and carcinoma; and multiple foci of PIN arise independently within the same prostate. This observation suggests that a field effect probably underlies prostatic neoplasia. Multiple foci of cancer also often arise independently, lending additional support to this hypothesis. The strong genetic similarities between PIN and cancer strongly suggest that evolution and clonal expansion of PIN, or other precursor lesions, may account for the multifocal etiology of carcinoma. Uncertainties with respect to identification of those precursor lesions which are most likely to progress to invasive and metastatic prostate cancer reinforce the requirement for objective immunohistochemical or molecular biological markers of the aggressive phenotype.

Frequent deletions at 11q23 and 13q14 in B cell prolymphocytic leukemia (B-PLL)

Deletions of the long arm of chromosomes 11 and 13 are the most frequent structural chromosome aberrations in various types of lymphoproliferative disorders. However, these regions have not been studied so far in B cell prolymphocytic leukemia (B-PLL). We have investigated the incidence of 13q deletions in 18 B-PLL cases by fluorescence in situ hybridization (FISH), using molecular probes for the RB1 and D13S25 loci. Chromosome 11q deletions were evaluated by FISH using the yeast artificial chromosome (YAC) clone 755b11 from the chromosome 11q22.3-q23.1 region, which has been previously shown to be deleted in 20% of cases of chronic lymphocytic leukemia. Chromosome 11q23 deletions were found in 7/18 (39%) cases of B-PLL. Monoallelic loss of RB1, D13S25 and BRCA2 was present in 10/18 (55%), 6/18 (33%) and 3/18 (16%) of the cases, respectively. All the cases with D13S25 and BRCA2 deletion showed RB1 loss. Deletions of 13q14 and 11q23 are frequent chromosome aberrations in B-PLL and, in contrast to CLL, there is a preferential loss of RB1 with respect to the D13S25 locus suggesting that allelic loss of the RB1 gene may play a role in the pathogenesis of B-PLL.

Expression of p53 and retinoblastoma gene in high-grade nodal peripheral T-cell lymphomas: immunohistochemical and molecular findings suggesting different pathogenetic pathways and possible clinical implications

The expression of p53 and the retinoblastoma gene has been investigated by immunohistochemical and molecular analysis in 45 cases of nodal peripheral T-cell lymphoma with high-grade histology. Most cases (73.3 per cent) were primary nodal lymphomas without any extra-nodal site involvement. Most of them (75.6 per cent) were histologically classified as pleomorphic, small, medium, and large cell type. Immunohistochemistry detected p53 in nine cases (20 per cent). In each of these cases, the polymerase chain reaction (PCR)/heteroduplex analysis did not show the presence of mutations, this finding being consistent with an alteration of the p53 functional pathway, in the presence of a wild-type protein. The retinoblastoma gene product was detected by immunohistochemistry in 35 cases (77.8 per cent) and not detected in ten cases (22.2 per cent). In the latter cases, the reverse transcription (RT)-PCR analysis showed the presence of a specific retinoblastoma gene transcript in six cases and was negative in the remaining four cases. The immunohistochemical and molecular findings seem to be consistent with abnormalities of retinoblastoma gene expression at either the transcriptional or the post-transcriptional level. Since all nine p53-positive cases by immunohistochemical analysis were also retinoblastoma gene product-positive, and all ten retinoblastoma gene product-negative cases were also p53-negative, two different and mutually exclusive pathways of possible pathogenetic significance may be suggested, the former involving abnormalities of the functional pathway of p53 in the absence of mutations and the latter abnormalities of retinoblastoma gene expression at the transcriptional and/or post-transcriptional level. Finally, the clinico-pathological correlations showed that p53 immunohistochemical expression is significantly associated with a poorer response to intensive chemotherapy.

Molecular pathogenesis of acromegaly

Acromegaly is generally caused by growth hormone (GH) hypersecretion from a benign, monoclonal pituitary adenoma. As in other neoplastic conditions, pituitary tumor formation and dysregulated hormone secretion are most likely the ultimate result of a series of genetic alterations. A number of molecular and biochemical defects have been associated with pituitary tumorigenesis. Molecular events such as tumor suppressor gene inactivation and oncogene activation involved in pituitary tumor progression are examined. The role of hypothalamic regulatory hormones and hereditary syndromes involving acromegaly are also discussed.

Level of retinoblastoma protein expression correlates with p16 (MTS-1/INK4A/CDKN2) status in bladder cancer

Recent studies have shown that patients whose bladder cancer exhibit overexpression of RB protein as measured by immunohistochemical analysis do equally poorly as those with loss of RB function. We hypothesized that loss of p16 protein function could be related to RB overexpression, since p16 can induce transcriptional downregulation of RB and its loss may lead to aberrant RB regulation. Conversely, loss of RB function has been associated with high p16 protein expression in several other tumor types. In the present study RB negative bladder tumors also exhibited strong nuclear p16 staining while each tumor with strong, homogeneous RB nuclear staining were p16 negative, supporting our hypothesis. To expand on these immunohistochemical studies additional cases were selected in which the status of the p16 encoding gene had been determined at the molecular level. Absent p16 and high RB protein expression was found in the tumors having loss of heterozygosity within 9p21 and a structural change (mutation or deletion) of the remaining p16 encoding gene allele, confirming the staining results. These results strongly support the hypothesis that the RB nuclear overexpression recently associated with poor prognosis in bladder cancer is also associated with loss of p16 function and implies that loss of p16 function could be equally deleterious as RB loss in bladder and likely other cancers.

Retinoblastoma (RB1) gene product expression in breast carcinoma. Correlation with Ki-67 growth fraction and biopathological profile

AIMS

To investigate the expression of retinoblastoma protein (pRb) in invasive breast tumours and compare its expression with the major biopathological prognostic indicators to identify more aggressive subgroups.

MATERIAL

Archival paraffin embedded tissues from 153 consecutive primary breast carcinomas.

METHODS

pRb, Ki-67, and oestrogen receptor/progesterone receptor proteins were identified by immunohistochemistry and score values were recorded by image cytometric analysis; p53 and EGFr expression was also evaluated.

RESULTS

pRb scores correlated strongly with proliferation activity as determined by Ki-67 staining. Positive relations were also observed between pRb scores, tumour size, nuclear and histological grade, and oestrogen receptor/progesterone receptor content, while abnormal p53 accumulation was not associated with pRb expression. Among the high proliferating carcinomas it was possible to identify 13 cases with loss of pRb expression.

CONCLUSIONS

pRb expression paralleled proliferative activity in the majority of breast carcinomas examined, suggesting that in these cases the protein behaves normally in regulating the cell cycle. Conversely in cases with loss of pRb immunostaining, the combined expression of specific highly aggressive factors (EGFr and p53 expression, oestrogen receptor/progesterone receptor negative status, and high K67) seems to characterise a more aggressive phenotype showing growth advantage and cellular "progression" rather than significant nodal involvement.

Expression of the retinoblastoma tumor suppressor gene (RB-1) in acute leukemia

In this report we review current studies concerning the RB-1 gene expression in acute leukemias. The RB-1 gene was analyzed in several studies by protein-, RNA and DNA-techniques in acute lymphoblastic leukemia (ALL) as well as in acute myelogenous leukemia (AML). The frequency of RB-1 inactivation in ALL-patients ranged between 30% and 64% in several studies. Structural abnormalities of the RB-1 gene were reported in 18% of ALL-patients and in 27% of Philadelphia chromosome-positive ALL, respectively. The proportion of AML-patients with absent RB-1 protein expression ranged between 19% and 55%. Structural RB-1-abnormalities in AML were predominantly reported in leukemias with monocytic differentiation. Furthermore, the prognostic value of an abnormal RB-1 gene expression was also estimated in some studies. In childhood ALL RB-1 inactivation was reported to have prognostic significance while in contrast, in another study on adults no prognostic value of RB-1 was found. In 4 out of 5 documented studies AML-patients with RB-1 inactivation generally had a poorer prognosis. In conclusion, RB-1 inactivation is frequently observed in acute leukemia. The prognostic value of low RB-1 expression is controversial but the majority of published studies found low RB-1 expression to be a negative prognostic predictor, in acute leukemia.

A deletion polymorphism due to Alu-Alu recombination in intron 2 of the retinoblastoma gene: association with human gliomas

The retinoblastoma gene (RB) encodes a tumor suppressor that is inactivated in a number of different types of cancer. We searched for gross alterations of this gene in tumors of the central nervous system by using Southern blot hybridization. A common alteration was found in several tumors and was mapped to the region around exon 2. Nucleotide sequencing showed that the alteration was caused by a 799-bp deletion in intron 2 of the RB gene and was probably due to homologous recombination between two Alu repeats. Deletions of this type have not been found previously in the RB gene. The deletion turned out to be a polymorphism with an allele frequency estimated at 2.2% in 185 patients without cancer. The deletion was found in five of 48 patients with brain tumors (allele frequency of 5.2%). This difference is not statistically significant (P = 0.149, Fisher's exact test). Confining the analysis only to glioma brain tumors revealed a statistically significant difference compared with the cancer-free patient controls (P = 0.027, Fisher's exact test). Further study is needed to determine if the deletion is a weak brain cancer-predisposing mutation or a harmless polymorphism. Finding this mutation in a tumor and the germline DNA of a retinoblastoma patient could lead to incorrect estimation of the heritability of a tumor.

Adrenocortical neoplasms: role of prognostic markers MIB-1, P53, and RB

Differentiation between benign and malignant adrenocortical neoplasms is made using a combination of clinical and pathologic parameters. Despite these parameters, it is still difficult to predict the biologic potential of some tumors. Forty adrenocortical lesions, including 10 hyperplasias, 10 adenomas, 12 carcinomas and eight metastatic/recurrent adrenocortical carcinomas were studied for the expression of MiB-1, p53, and the retinoblastoma gene product (RB) utilizing immunohistochemical techniques. The mean tumor proliferating fraction (TPF), expressed as the number of MiB-1-positive nuclei per 1,000 tumor cells, was 14.9 in adenomas, 31.5 in hyperplasias, 208.1 in carcinomas and 166.1 in recurrent or metastatic disease. None of the 20 benign lesions had a TPF of > 80, and only one of the 20 malignancies had a TPF of < 80. Nine of the 20 carcinomas were positive for p53. None of the benign lesions were p53 positive. Thirty-nine cases, including benign and malignant ones, were RB positive, and one was uninterpretable. We conclude that prognostic markers can be of great assistance in recognizing adrenocortical carcinomas. High TPF (> 80), as measured by staining with MiB-1, and positive p53 strongly correlate with malignant behavior and therefore may be useful in distinguishing benign from malignant adrenal lesions. Staining for RB does not appear to be a helpful technique.

Allelic deletion in pituitary adenomas reflects aggressive biological activity and has potential value as a prognostic marker

Tumors of the pituitary gland are usually benign adenomas and account for 10% of all intracranial neoplasms. Five pituitary tumors have previously been reported to harbor multiple allelic deletions. Of these, three displayed particularly aggressive biological behavior, whereas there were no clinical details provided for the others. This study was designed to test the hypothesis that genetic deletions are a marker of invasive behavior and to identify the loci most commonly involved. Accordingly, we studied two cohorts of pituitary tumors, classified radiologically as invasive or noninvasive, for loss of heterozygosity (LOH). There is a significantly higher frequency of LOH in invasive tumors (10.8% of all loci examined) compared to noninvasive tumors (2.4%; P < 0.001). Of the 11 loci investigated, 75% of the allelic deletions identified in invasive tumors were found at 4 loci: 11q13, 13q12-14, 10q, and 1p. Twenty of 47 invasive tumors had evidence of at least 1 allelic deletion, whereas 14 of 20 had more than 1. Of the 6 tumors with only 1 deletion, 5 involved the 11q13 locus, suggesting that this is an early change in the transition from noninvasive to invasive adenoma. Comparison of invasive and noninvasive tumors demonstrates a significantly higher frequency of deletions affecting 11q13 (P < 0.001), 13q12-14 (P < 0.05), and 10q26 (P < 0.05) in invasive tumors. In addition, allelic deletion correlates with increasingly invasive behavior (modified Hardy classification), as 73% of grade 4 tumors compared to 33% of grade 3 and 9.5% of grade 1 and 2 tumors demonstrated LOH at any locus. Furthermore, in some tumors we identified a breakpoint between markers intragenic and extragenic to the retinoblastoma gene (Rb1) on chromosome 13q, suggesting that tumor suppressor genes other than or in addition to Rb1 may be involved in pituitary tumorigenesis. This was further supported by the presence of Rb protein in two of four tumors where the genetic loss extended to include the intragenic marker D13S153. Early identification of tumors with likely invasive potential by means of genetic analysis (LOH) may provide useful information on potential tumor behavior and aid tumor management in a manner that is not possible using routine histological methods. A large prospective study is required in patients without radiological evidence of invasion to assess the value of LOH in predicting outcome and for planning treatment.

Deletion of three distinct regions on chromosome 13q in human non-small-cell lung cancer

We examined loss of heterozygosity (LOH) at the retinoblastoma susceptibility gene (RB1) locus on chromosome 13q14 in 20 non-small-cell lung cancers (NSCLCs) using polymorphic markers. The expression of RB protein was examined by immunohistochemical analysis of paraffin-embedded specimens of the same tumors. The results revealed that 10 of 16 informative cases showed an LOH at the RB1 locus, whereas only 2 of the 10 tumors lost expression of the RB protein. These 2 tumors had mutations in the remaining RB1 allele. Thus, inactivation of the RB1 gene appears to be involved in a small subset of NSCLCs only. To elucidate the presence of tumor-suppressor genes other than RB1 on 13q, heterozygosity at 15 different loci was investigated. Of 20 tumors analyzed, 15 showed an LOH at least at one locus, and the regions 13q12.1-qter, 13q12.2-14.2 and 13q14.1-q14.3, including the RB1 locus, were deleted in significant numbers of the tumors. Our results suggest that, in addition to the RB1 gene, abnormalities of other tumor-suppressor genes on chromosome 13q are involved in the development of human NSCLCs.

Differential retinoblastoma protein expression in neuroendocrine tumors of the lung. Potential diagnostic implications

Neuroendocrine lung tumors have been considered by some to be a continuum ranging from relatively benign typical carcinoids to highly malignant small-cell carcinomas. Histopathological diagnosis may sometimes be difficult because of their overlapping features. Correct classification, however, carries important prognostic and therapeutic significance. To determine the clinicopathological implications of retinoblastoma (RB) protein expression in these neoplasms, we examined the RB status in a series of neuroendocrine tumors by immunohistochemical analysis of paraffin-embedded tissue sections. A total of 105 tumors were studied. All 44 typical and 15 atypical carcinoids, one of which was initially misdiagnosed as a small-cell carcinoma, manifested a heterogeneous RB-positive staining pattern. Atypical carcinoids in general showed an increase in the number of tumor cells with strong nuclear staining compared to typical carcinoids. In contrast, all 40 small-cell and 6 large-cell neuroendocrine carcinomas failed to show RB staining in any tumor nuclei, indicating loss of RB function. Our results suggest that RB status as measured by immunohistochemical staining can be used as a marker to distinguish typical and atypical carcinoids from small-cell and large-cell neuroendocrine carcinomas.

High levels of MDM2 are not correlated with the presence of wild-type p53 in human malignant mesothelioma cell lines

Prior analysis of 20 human mesothelioma cell lines for p53 status revealed only two mutations and one p53 null cell line, although p53 expression was detected in most cell lines. In addition, mRNA and protein expression of the retinoblastoma gene product in human mesothelioma cell lines is similar to normal controls. We have tested for p53 induction after exposure to ionising radiation and demonstrate this induction and, to a lesser extent, p21(WAF1) induction, in both normal mesothelial cells and p53-positive mesothelioma cell lines. We postulated that high levels of MDM2 might alter p53 and retinoblastoma tumour-suppressor function in mesothelioma. However, Southern blot analysis for mdm2 indicated that no amplification had occurred in 18 mesothelioma cell lines tested. Steady-state mRNA and protein levels also did not indicate overexpression. These results indicate that high levels of MDM2 are not responsible for inactivating the functions of wild-type p53 or the retinoblastoma gene product during the pathogenesis of malignant mesothelioma.

Involvement of the cyclin-dependent kinase-4 inhibitor (CDKN2) gene in the pathogenesis of lymphoid blast crisis of chronic myelogenous leukaemia

Recent data suggest that homozygous deletion of the cyclin-dependent kinase 4 inhibitor gene (CDKN2), a putative tumour suppressor gene located on chromosome 9p21, represents a common genetic event in human cancer. As the molecular basis of the evolution of chronic myelogenous leukaemia (CML) into blast crisis remains largely unknown, we decided to investigate if the occurrence of similar deletions could represent one of the mechanisms underlying the disease progression. Whereas none of 22 chronic phase CML cases examined showed alterations, we found that 3/17 total blast crisis examined (18%) showed a homozygous deletion of the CDKN2 gene. The deletions were restricted to cases of lymphoid blast crisis, being present in 3/8 (40%) of the lymphoid and in none of the nine myeloid cases examined. The fact that the chronic phase DNA obtained at diagnosis in one of the cases lacks the homozygous deletion observed in blast crisis, suggests that the final deletion event took place concomitantly with the progression of the disease. Furthermore, the analysis of polymorphic regions on chromosome 9p21 flanking at both sides the CDKN2 gene, showed that deletions at 9p21 differ between cases and are characterized by a wide range of extensions. A concomitant search for a possible involvement of the p53 tumour suppressor gene in the same series of patients showed mutations of the gene and loss of heterozygosity at 17p only in myeloid blast crisis, suggesting the presence of distinct molecular pathways in the pathogenesis of lymphoid and myeloid blast crisis.

Inactivation of retinoblastoma gene in malignant parathyroid growths: a candidate genetic trigger?

The molecular basis for parathyroid carcinoma remains undetermined. Parathyroid carcinoma potentially remains curable by early en bloc resection. This requires a reliable diagnostic tool as histological features alone are insufficient to distinguish parathyroid carcinoma from its benign counterpart, parathyroid adenoma. A variety of human cancers arise from the inactivation of the retinoblastoma (RB) gene, a tumour-suppressor gene on chromosome 13q14. We investigated the role of this gene in parathyroid growths by using a mouse monoclonal antibody to detect RB gene expression immunohistochemically. Two of the three parathyroid carcinomas in this study showed evidence of RB gene inactivation compared with one of 11 benign parathyroid entities. Three normal parathyroid glands stained showed strong evidence of RB gene expression in all three glands. The relationship between RB gene inactivation and parathyroid malignancy, however, was not statistically significant.

Genetic analysis of chromosome 13 deletions in BCR/ABL negative chronic myeloproliferative disorders

Chromosomal deletions of band 13q14 occur recurrently in BCR/ABL negative chronic myeloproliferative disorders (CMPD), including myelosclerosis with myeloid metaplasia (MMM), polycythemia vera (PV), essential thrombocythemia (ET), juvenile chronic myeloid leukemia (JCML), and the so-called BCR/ABL- chronic myeloid leukemia (CML). The RBI tumor suppressor locus, mapping to 13q14, has long since been hypothesized as the important gene. In this report, we have determined the frequency of 13q14 deletions at the molecular level in a large panel of BCR/ABL- CMPD at different disease stages and performed a detailed genetic analysis of gross rearrangements/deletions and point mutations of the RBI gene in these disorders. Our data show that molecular deletions of 13q14 are detected in a relatively large fraction of BCR/ABL- CMPD (38%), that they appear to be more frequent in MMM than in other BCR/ABL- CMPD, and that they may be present at diagnosis or occur during blastic evolution of the neoplasia. The RBI gene displayed a germline configuration in all BCR/ABL- CMPD tested, suggesting that 13q14 deletions in these disorders affect a tumor suppressor locus distinct from RBI.

Mutations of cell cycle regulators. Biological and clinical implications for human neoplasia

Neoplastic diseases are characterized by uncoordinated cell growth. Cellular proliferation follows an orderly progression through the cell cycle, which is governed by protein complexes composed of cyclins and cyclin-dependent kinases. These complexes exert their regulatory function by phosphorylation of key proteins involved in cell cycle transitions, such as the product encoded by the retinoblastoma gene (pRB). Mutations and overexpression of cyclins and cyclin-dependent kinases, mainly cyclin D1 and Cdk4, have been reported and proposed to be oncogenic events. More recently, a new family of negative regulators functioning as Cdk-inhibitory molecules has been identified. Because of their recessive nature in cell cycle control and the fact that some of them are mutated in human tumors, it has been suggested that they may also function as tumor suppressor genes. It appears that the molecular networking of these proteins and complexes impact on two fundamental cell cycle regulators: p53 and pRB. Cross-talk pathways between these two nuclear proteins are being delineated, implying potential links between p53 and pRB in cell cycle control, apoptosis, and tumor progression. In addition, the high rate and mutation pattern of TP53 and RB in primary tumors have rendered them prototype tumor suppressor genes. Furthermore, detection of TP53 and RB mutations and altered expression of their encoded products appear to be of clinical significance, often correlating with prognosis, when identified in specific cancers. Based on these findings, new strategies are being developed in the emerging field of gene replacement-therapy.

Immunohistochemical features of the human retina and retinoblastoma

The immunohistochemical features of 24 retinoblastoma specimens from 22 patients, 15 with unilateral and 7 with bilateral disease, were examined by the labelled streptavidin biotin (LSAB) method and compared with those of specimens from the remaining morphologically normal retina. In the normal retina, S-100 protein, glial fibrillary acidic protein (GFAP) and vimentin were detected in astrocytes and/or Müller cells. Neurofilament protein was seen in axons of the ganglion cells, synaptophysin was present in both plexiform layers, bcl-2 oncoprotein was seen in ganglion cells and bipolar cells, and neuron-specific enolase (NSE) was detected in ganglion cells, bipolar cells and photoreceptor cells and in their cell processes. While retinoblastoma (Rb) protein expression was noted in ganglion cells, bipolar cells, and some photoreceptor cells, p53 protein was not expressed at all. In all retinoblastomas, strong NSE expression and weak bcl-2 expression was observed in almost all tumour cells and synaptophysin was localized in rosette-forming cells, while tumour cells were devoid of S-100, GFAP, vimentin and neurofilament protein. These findings support the view that retinoblastomas are composed of neuron-committed cells. In addition, no Rb protein expression was detected in retinoblastomas, whereas p53 expression was found in 18 cases (75%).

Loss of heterozygosity in chondrosarcomas for markers linked to hereditary multiple exostoses loci on chromosomes 8 and 11

Hereditary multiple exostoses (EXT; MIM 133700) is an autosomal dominant condition characterized by growth of multiple benign cartilage-capped tumors. EXT greatly increases the relative risk to develop chondrosarcoma, although most chondrosarcomas are sporadic. This observation suggests that, like the genes responsible for retinoblastoma and other dominantly inherited cancer susceptibility disorders, the genes that cause EXT may have tumor-suppressor function and may play a role in the pathogenesis of the related sporadic tumors. To investigate this hypothesis, we evaluated chondrosarcomas for loss of constitutional heterozygosity (LOH) at polymorphic loci linked to three recently identified genomic regions containing genes involved in EXT. LOH for markers linked to EXT1 on chromosome 8 was detected in a chondrosarcoma that arose in a man with EXT. Four of 17 sporadic tumors showed LOH for markers linked to EXT1, and 7 showed LOH for markers linked to EXT2 on chromosome 11. In all, LOH was observed for markers linked to EXT1 or EXT2 in 44% of the 18 tumors, whereas heterozygosity was retained for markers on 19p linked to EXT3. These findings support the hypothesis that genes on 8q and the pericentromeric region of 11 have tumor-suppressor function and play a role in the development of chondrosarcomas.

The spinal cord as an alternative model for nerve tissue graft

The spinal cord provides an alternative model for nerve tissue grafting experiments. Anatomo-functional correlations are easier to make here than in any other region of the CNS because of a direct implication of spinal cord neurons in sensorimotor activities. Lesions can be easily performed to isolate spinal cord neurons from descending inputs. The anatomy of descending monoaminergic systems is well defined and these systems offer a favourable paradigm for lesion-graft experiments.

Multiple obstacles to gene therapy in the brain

Neuwelt et al. have proposed gene-transfer experiments utilizing an animal model that offers many important advantages for investigating the feasibility of gene therapy in the human brain. A variety of tissues concerning the viral vector and mode of delivery of the corrective genes need to be resolved, however, before such therapy is scientifically supportable.

Principles of brain tissue engineering

It is often presumed that effects of neural tissue transplants are due to release of neurotransmitter. In many cases, however, effects attributed to transplants may be related to phenomena such as trophic effects mediated by glial cells or even tissue reactions to injury. Any conclusion regarding causation of graft effects must be based on the control groups or other comparisons used. In human clinical studies, for example, comparing the same subject before and after transplantation allows for many interpretations of the causes of clinical changes.