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Background To improve their standing in residency selection, many osteopathic medical students choose to take the United States Medical Licensing Examination (USMLE). Although scores on USMLE Step 1 and Level 1 of the Comprehensive Osteopathic Medical Licensing Examination (COMLEX-USA) are known to be highly correlated, scarce data exist on the association between COMLEX-USA Level 2-Cognitive Evaluation (CE) and USMLE Step 2 Clinical Knowledge (CK) scores. In this study, we aimed to determine the association between COMLEX-USA Level 2-CE and USMLE Step 2 CK scores and derive an equation to predict performance on USMLE Step 2 CK for applicants who have only taken COMLEX-USA. Methodology We reviewed COMLEX-USA Level 2-CE and USMLE Step 2 CK scores for all students at the Lake Erie College of Osteopathic Medicine from May 2020 to April 2021. Linear regression was used to evaluate the relationship between COMLEX-USA Level 2-CE and USMLE Step 2 CK scores. Results A total of 340 students took both COMLEX-USA Level 2-CE and USMLE Step 2 CK. There was a linear association between COMLEX-USA Level 2-CE and USMLE Step 2 CK scores such that every one-point increase in COMLEX-USA was associated with a 0.13-point increase in USMLE Step 2 CK score (standard error = 9.1; model R 2 = 0.64). Conclusions Students or programs interested in predicting performance on USMLE Step 2 CK from performance on COMLEX-USA Level 2-CE can do so using the following equation: USMLE Step 2 CK = 0.13(COMLEX-USA Level 2-CE) + 163.5., Competing Interests: The authors have declared that no competing interests exist., (Copyright © 2021, Smith et al.)

Introduction The reliance on the United States Medical Licensing Examination (USMLE) Step 1 scores in residency selection creates problems for osteopathic medical students and the programs that review their applications. Although many osteopathic students take the USMLE to improve their standing for residency selection, students who score poorly may harm their candidacy. Simultaneously, programs unfamiliar with the Comprehensive Osteopathic Medical Licensing Examination (COMLEX-USA) may struggle to evaluate applicants who have not taken USMLE. Objective To determine the association between COMLEX-USA Level 1 and USMLE Step 1 scores and derive an equation that could be used to predict USMLE performance or approximate USMLE scores for applicants who have only taken COMLEX-USA. Methods We reviewed COMLEX-USA Level 1 and USMLE Step 1 scores for all students at the Lake Erie College of Osteopathic Medicine (LECOM), Bradenton campus, from January 2012 until December 2016. Linear regression was used to evaluate the relationship between COMLEX-USA Level 1 and USMLE Step 1 scores. Results Overall, 2097 students took both examinations during the study period. Every one-point increase in COMLEX-USA was associated with a 0.15 point increase in USMLE Step 1 score (standard error 11.5; model R 2 0.56). On average, students scored 30 percentile points lower on USMLE Step 1 than on COMLEX-USA, and 24% of students scoring <500 on COMLEX-USA Level 1 failed USMLE Step 1. Conclusions Students or programs interested in predicting performance on USMLE Step 1 from performance on COMLEX-USA Level 1 can do so with the following equation: USMLE Step 1 = 0.15 (COMLEX-USA Level 1) + 138.7., Competing Interests: The authors have declared that no competing interests exist., (Copyright © 2021, Smith et al.)

Inactivation of the von Hippel-Lindau (VHL) gene is associated with the development of highly vascularized tumors. pVHL targets the alpha subunits of hypoxia inducible factor (HIF) for ubiquitin-mediated degradation in an oxygen-dependent manner. Although pVHL-deficient tumor cell lines demonstrate constitutive stabilization and activation of HIF, it has yet to be shown that loss of murine Vhl alone is sufficient to dysregulate HIF. We utilized a genetic approach to demonstrate that loss of Vhl is sufficient not only to stabilize HIF-alpha subunits under normoxia, but also fully activate HIF-mediated responses. These studies have implications for the hierarchy of signaling events leading to HIF stabilization, nuclear translocation, and target gene expression. We further demonstrate that loss of murine Vhl does not promote teratocarcinoma growth, indicating that other genetic changes must occur to facilitate Vhl-mediated tumorigenesis.

Background: Adp27(Kip1), a recombinant adenovirus, was evaluated for expression of p27, a cyclin-dependent kinase inhibitor (CDKI) and tumor suppressor protein, in human prostate carcinoma cells. Effects of p27(Kip1) on cell cycle and apoptosis were analyzed., Methods: We evaluated the effects of overexpression of p27(Kip1) in the human prostate carcinoma cell lines LNCaP, DU-145, and PC-3 in vitro and in vivo. Growth curve studies, cell cycle analysis, terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL), and annexin V-fluorescein isothiocyanate apoptosis analyses were conducted to determine effects of p27(Kip1) on cell cycle. CDKI activity assays and Western blots were conducted to determine presence/activities of CDKIs., Results: Adp27(Kip1)-induced protein levels increased in a dose-dependent manner; p27(Kip1) protein was detected within 6 hr of infection with Adp27(Kip1) and remained stable for at least 48 hr. The activities of Cdk2, Cdk4, and Cdc2 kinases were inhibited 24 hr after infection with Adp27(Kip1). Bromodeoxyuridine incorporation demonstrated a dose-dependent decrease in S-phase cells 24 hr postinfection. TUNEL analysis revealed an induction of apoptosis (10 pfu/cell) within 48 hr of infection in all cell lines. Growth curve analyses demonstrated that Adp27(Kip1) infection inhibited proliferation of all cell lines tested and decreased cell numbers for Adp27(Kip1)-infected LNCaP and PC-3 cells by 96 hr. Cell cycle analysis of DNA content demonstrated an accumulation of cells in G0/G1-phase 24-120 hr after Adp27(Kip1)-infection. In vivo studies demonstrated a reduction in LNCaP xenograft tumor growth rates in mice injected with Adp27(Kip1)., Conclusion: Exogenous p27(Kip1) overexpression results in cell cycle regulation in the human prostate carcinoma cell lines tested, representing the first use of this vector on prostate cancer cell lines in vitro and in vivo. Moreover, p27(Kip1) expression is associated with an increase in early apoptosis, which represents a recently discovered function for this protein. It also represents the first time this association has been observed in prostate carcinoma cell lines. This study provides support for the further development of Adp27(Kip1) as a potential therapeutic vector in the treatment of adenocarcinoma of the prostate., (Copyright 2002 Wiley-Liss, Inc.)

Mutations of the VHL tumor suppressor gene occur in patients with VHL disease and in the majority of sporadic clear cell renal carcinomas (VHL(-/-) RCC). Loss of VHL protein function is associated with constitutive expression of mRNAs encoding hypoxia-inducible proteins, such as vascular endothelial growth factor. Overproduction of angiogenic factors might explain why VHL(-/-) RCC tumors are so highly vascularized, but whether this overproduction is sufficient for oncogenesis still remains unknown. In this report, we examined the activity of transforming growth factor-alpha (TGF-alpha), another VHL-regulated growth factor. We show that TGF-alpha mRNA and protein are hypoxia-inducible in VHL(-/-) RCC cells expressing reintroduced VHL. In addition to its overexpression by VHL(-/-) RCC cells, TGF-alpha can also act as a specific growth-stimulatory factor for VHL(-/-) RCC cells expressing reintroduced wild-type VHL, as well as primary renal proximal tubule epithelial cells, the likely site of origin of RCC. This role is in contrast to those of other growth factors overexpressed by VHL(-/-) RCC cells, such as vascular endothelial growth factor and TGF-beta1, which do not stimulate RCC cell proliferation. A TGF-alpha-specific antisense oligodeoxynucleotide blocked TGF-alpha production in VHL(-/-) RCC cells, which led to the dependence of those cells on exogenous growth factors to sustain growth in culture. Growth of VHL(-/-) RCC cells was also significantly reduced by a drug that specifically inhibits the epidermal growth factor receptor, the receptor through which TGF-alpha stimulates proliferation. These results suggest that the generation of a TGF-alpha autocrine loop as a consequence of VHL inactivation in renal proximal tubule epithelial cells may provide the uncontrolled growth stimulus necessary for the initiation of tumorigenesis.

Purpose: Families with von Hippel-Lindau disease have variable risk of pheochromocytoma. Patients with von Hippel-Lindau disease and pheochromocytoma identified by screening can have no characteristic signs or symptoms. Families with von Hippel-Lindau disease were screened and followed to describe the natural history of von Hippel-Lindau pheochromocytoma, and to correlate these findings with von Hippel-Lindau germline mutation., Materials and Methods: Between 1988 and 1997, 246 individuals with von Hippel-Lindau disease were identified (von Hippel-Lindau group). Between August 1990 and June 1997, 26 consecutive patients with sporadic pheochromocytoma were evaluated (sporadic group)., Results: A total of 64 patients with von Hippel-Lindau disease had manifestations of pheochromocytoma, including 33 newly diagnosed during screening at the National Institutes of Health and 31 previously treated (93 adrenal and 13 extra-adrenal pheochromocytomas). Germline von Hippel-Lindau gene missense mutation was associated with extra-adrenal pheochromocytoma, younger age at presentation and the only patient with metastases. Of the 33 newly diagnosed patients with von Hippel-Lindau disease 4 had pheochromocytoma 2 times (37 pheochromocytomas) during followup. Of these pheochromocytomas 35% (13 of 37) were associated with no symptoms, normal blood pressure and normal catecholamine testing. Comparison of urinary catecholamines in the von Hippel-Lindau and sporadic groups demonstrated increased epinephrine, metanephrines and vanillylmandelic acid in the sporadic group. Analysis of urinary catecholamine excretion in the von Hippel-Lindau and sporadic groups together demonstrated a correlation between tumor size, and urinary metanephrines, vanillylmandelic acid, norepinephrine, epinephrine and dopamine. In 12 patients without signs or symptoms of pheochromocytoma 17 newly diagnosed pheochromocytomas were followed for a median of 34.5 months without morbidity. Median tumor doubling time was 17 months., Conclusions: Von Hippel-Lindau gene missense mutation correlated with the risk of pheochromocytoma in patients with von Hippel-Lindau disease. These findings support a von Hippel-Lindau disease clinical classification, wherein some families are at high risk for manifestations of pheochromocytoma. Von Hippel-Lindau disease pheochromocytomas identified by screening were smaller and less functional than sporadic pheochromocytomas.

Loss of function in the von Hippel-Lindau (VHL) tumor suppressor gene occurs in familial and most sporadic renal cell carcinomas (RCCs). VHL has been linked to the regulation of cell cycle cessation (G(0)) and to control of expression of various mRNAs such as for vascular endothelial growth factor. RCC cells express the Met receptor tyrosine kinase, and Met mediates invasion and branching morphogenesis in many cell types in response to hepatocyte growth factor/scatter factor (HGF/SF). We examined the HGF/SF responsiveness of RCC cells containing endogenous mutated (mut) forms of the VHL protein (VHL-negative RCC) with that of isogenic cells expressing exogenous wild-type (wt) VHL (VHL-positive RCC). We found that VHL-negative 786-0 and UOK-101 RCC cells were highly invasive through growth factor-reduced (GFR) Matrigel-coated filters and exhibited an extensive branching morphogenesis phenotype in response to HGF/SF in the three-dimensional (3D) GFR Matrigel cultures. In contrast, the phenotypes of A498 VHL-negative RCC cells were weaker, and isogenic RCC cells ectopically expressing wt VHL did not respond at all. We found that all VHL-negative RCC cells expressed reduced levels of tissue inhibitor of metalloproteinase 2 (TIMP-2) relative to the wt VHL-positive cells, implicating VHL in the regulation of this molecule. However, consistent with the more invasive phenotype of the 786-0 and UOK-101 VHL-negative RCC cells, the levels of TIMP-1 and TIMP-2 were reduced and levels of the matrix metalloproteinases 2 and 9 were elevated compared to the noninvasive VHL-positive RCC cells. Moreover, recombinant TIMPs completely blocked HGF/SF-mediated branching morphogenesis, while neutralizing antibodies to the TIMPs stimulated HGF/SF-mediated invasion in vitro. Thus, the loss of the VHL tumor suppressor gene is central to changes that control tissue invasiveness, and a more invasive phenotype requires additional genetic changes seen in some but not all RCC lines. These studies also demonstrate a synergy between the loss of VHL function and Met signaling.

Inheritance of an inactivated form of the VHL tumor suppressor gene predisposes patients to develop von Hippel-Lindau disease, and somatic VHL inactivation is an early genetic event leading to the development of sporadic renal cell carcinoma. The VHL gene was disrupted by targeted homologous recombination in murine embryonic stem cells, and a mouse line containing an inactivated VHL allele was generated. While heterozygous VHL (+/-) mice appeared phenotypically normal, VHL -/- mice died in utero at 10.5 to 12.5 days of gestation (E10.5 to E12.5). Homozygous VHL -/- embryos appeared to develop normally until E9.5 to E10.5, when placental dysgenesis developed. Embryonic vasculogenesis of the placenta failed to occur in VHL -/- mice, and hemorrhagic lesions developed in the placenta. Subsequent hemorrhage in VHL -/- embryos caused necrosis and death. These results indicate that VHL expression is critical for normal extraembryonic vascular development.

Central nervous system hemangioblastoma is a neoplasm with characteristic and well-described histopathological features, including proliferation of vascular and stromal cells. yet, the histogenesis of the stromal cell component and its neoplastic capacity as compared with the vascular component are still controversial. Stromal cells were selectively procured from formalin-fixed, paraffin-embedded archival tissue from a von Hippel-Lindau (VHL) disease patient with a cerebellar hemangioblastoma and studied for loss of heterozygosity (LOH) of the VHL gene locus and associated microsatellite regions. The stromal cells consistently showed LOH. Analysis of mixed stromal anti vascular areas of this tumor and four other hemangioblastomas of VHL patients showed that loss of heterozygosity was partially obscured. These preliminary results suggest that the stromal component of hemangioblastomas contains genetic alterations consistent with a neoplastic nature. Additional samples of pure stromal cells need to be analyzed to establish the prevalence of VHL gene deletion in stromal cells of capillary hemangioblastoma and, hence, its pathogenetic significance.

Patients with von Hippel-Lindau (VHL) disease develop a spectrum of bilateral clear-cell renal lesions including cysts and renal cell carcinomas (RCCs). VHL gene deletions have been previously reported in VHL-associated macroscopic RCC. Although histological analysis suggests that microscopic cystic lesions in the VHL patients may represent precursors of the RCC, there is at present no direct molecular evidence of their relationship. To investigate the relationship between cystic lesions and RCC, 26 microdissected archival renal lesions from two VHL disease patients were studied for loss of heterozygosity at the VHL gene locus using polymerase chain reaction single-strand conformation polymorphism analysis. The renal lesions included 2 benign cysts, 5 atypical cysts, 5 microscopic RCCs in situ, 5 cysts lined by a single layer of cells, in which RCCs in situ were developing, and 2 microscopic and 7 macroscopic RCCs. Except for a single benign cyst, 25 of 26 renal lesions showed nonrandom allelic loss of the VHL gene. In either of the 2 patients, the same VHL allele was deleted in all of the lesions tested, indicating loss of the wild-type allele and retention of the inherited, mutated VHL allele. The results suggest that all clear-cell lesions in the VHL kidney represent neoplasms and that the loss of the VHL gene occurs early in their development. Atypical and benign cysts most likely represent the initial phenotype in malignant transformation to the RCC.

The von Hippel-Lindau (VHL) disease gene on chromosome 3p25.5 has been cloned and shown to be mutated in the germline DNA of patients with VHL disease. In addition, approximately 60% of sporadic renal cell carcinomas (RCCs) have been shown to have a VHL gene mutation in fresh frozen tumor tissue and tumor-derived cell lines. The objective of this study was to test whether VHL gene mutations could be detected in archival sporadic RCC cases. We studied three sporadic RCCs, two oncocytomas, and the corresponding adjacent normal renal parenchyma by polymerase chain reaction and single-strand conformation polymorphism analysis using paraffin-embedded, formalin-fixed material. Tumor and normal tissue were microdissected from eosin-stained 5-microns-thick histologic sections. Mutations in exon 2 of the VHL gene were detected in all three of the sporadic RCCs but were not observed in the matched normal renal tissues or in the two oncocytomas tested. The mutations were identical to those detected in tumor cell lines from the same patients. This report represents the first detection of VHL gene mutations in sporadic RCCs in archival, paraffin-embedded tissue. A high percentage of sporadic RCCs show VHL gene mutations in fresh frozen tissue but the availability of frozen material is limited, so the evaluation of archival tumors for similar mutations should prove useful in future RCC studies. Furthermore, the results suggest that the genetic events leading to the development of clinically benign renal oncocytoma may differ from those leading to malignant RCC.

The progression of human malignancies is thought to involve the inactivation or loss of tumor suppressor genes. Previous studies have suggested that inactivation of tumor suppressor genes on chromosomes 5q, 17p, 18q, and 8p play a role in the development of colorectal carcinoma. However, chromosome 3p at the von Hippel-Lindau disease (VHL) gene locus (3p25-26) has not been previously implicated in the development or progression of sporadic colorectal carcinoma. The authors have analyzed VHL gene alterations on chromosome 3p in sporadic human colon carcinomas and adenomas using modified microdissection techniques. These techniques allow for procurement and analysis of selected subpopulations of cells from both paraffin-embedded and frozen human tumor specimens. VHL disease gene deletion was detected by polymerase chain reaction (PCR) and single-strand conformation polymorphism (SSCP) analysis in microdissected colon carcinoma specimens. Allelic loss of VHL gene was detected in 7 of 11 (64%) informative patients who underwent colectomy for primary sporadic colon carcinoma. However, no allelic loss of VHL gene was shown in colonic adenomas of eight informative patients. These results indicate that VHL disease gene deletion frequently occurs in sporadic colon carcinoma. Because this deletion was not present in adenomas, VHL gene may play a role in colonic carcinogenesis and represent a relatively late event in colonic neoplasia progression. Additionally, microdissection of tissue sections may be especially useful in detecting allelic loss in PCR-based studies of infiltrating tumors, particularly when the tumor cells represent a relatively small percentage of the total cell population.

Renal cell carcinoma (RCC) is the most common malignancy in the adult kidney. Because RCC is generally thought to arise from the epithelium of the proximal tubules, the expression of Pax-2, a gene required for renal epithelium development, was examined in primary tumors and tumor-derived cell lines. Immunostaining of frozen sections from the primary tumors indicated Pax-2 expression in the malignant cells but not in the surrounding stroma. In a panel of human RCC-derived cell lines, 73% expressed Pax-2 protein and mRNA. Treatment of RCC cell lines with antisense oligodeoxynucleotides resulted in down-regulation of Pax-2 protein expression and growth inhibition after 3 days in culture. These data indicate that Pax-2 gene function is required for proliferation, as well as differentiation during embryonic development, and suggest a novel therapy for RCC.

Successful cytogenetic analysis was performed on 27 samples from 25 patients with RCC, including 7 of 11 tumors studied and 20 cell lines. Clonal chromosomal abnormalities were detected in all 27 samples. The most frequently involved chromosomes were 7, 1, 3, 9, and the Y (20, 17, 17, 14, and 10 cases, respectively). Polysomy 7 or rearrangement of 7q was seen in 80% (20/25) of the patients, and loss or rearrangement of 3p was seen in 48% (12/25); of the latter, four patients had loss of the whole chromosome and 10 patients had deletions or translocations involving 3p, with breakpoints at either 3p11-14 or 3p21-23 (5/7 translocation breakpoints were at 3p21-23). Loss of the sex chromosomes was seen in 15 patients, including -Y in 10/22 males. Other clonal changes included structural abnormalities of chromosome 1 centromere and the long arm, breakpoints at or near the centromere of chromosome 9 (10 patients), polysomy 16, monosomy 17, polysomy 20, and monosomy 22. With the exception of chromosome 3p loss, which was primarily confined to the nonpapillary cases, no specific clonal abnormality was noted for any particular subtype of RCC. Trisomy or tetrasomy 7 and -Y were seen in all subtypes of renal cell carcinoma.

Reduced expression of nm23 has been associated with increased metastases and decreased survival in a variety of malignancies. In the present study, the expression of nm23 was examined by Northern and Western blot analyses in a series of cell lines derived from patients with metastatic renal cell carcinoma. Two of twelve (17%) informative cell lines derived from 9 patients had loss of heterozygosity at Nm23-H1. Twenty-two renal cancer cell lines derived from primary tumors, 5 cell lines derived from metastatic tumors and 4 short-term cultures of normal proximal renal tubular cells all expressed Nm23 mRNA in varying amounts. On average, the level of expression of Nm23 mRNA in short-term cultures of benign proximal renal tubular cells was found to be similar to the level seen in renal cancer cell lines. Twenty-eight cell lines derived from renal primary tumors and 8 cell lines derived from metastatic tumors expressed both the Nm23-H1 and Nm23-H2 proteins. High or low relative expression of nm23 at the mRNA or protein level did not correlate with survival. The absence of any anomalous pattern of expression of the nm23 genes and the lack of correlation of expression with survival suggests that nm23 does not play a central role in the progression of this tumor type.

Pheochromocytomas occur sporadically and are associated with several dominantly inherited cancer syndromes, including von Hippel-Lindau (VHL) disease. We examined 14 pheochromocytomas (four from VHL patients, nine from sporadic patients, and one from a patient with familial pheochromocytoma) for loss of heterozygosity on chromosome arm 3p by using the polymerase chain reaction and restriction fragment length polymorphisms at eight loci. Loss of heterozygosity was detected in 8 of 14 pheochromocytomas examined: in three of the four VHL-associated tumors, in four of the nine sporadic tumors, and in the familial pheochromocytoma-associated tumor. Deletion of the inherited wild-type VHL allele was demonstrated in both informative VHL-associated pheochromocytomas, demonstrating involvement of VHL in pheochromocytoma development. However, because VHL mutations have not been detected in sporadic pheochromocytomas, VHL and/or another chromosome arm 3p gene may be involved in the etiology of these tumors.

Tumor suppressor genes have been found to have loss of function in a number of malignancies. This loss of function is believed to contribute to malignant transformation or metastatic spread. In the present study, expression of the retinoblastoma (RB) tumor suppressor gene was examined in cell lines and tumor tissue obtained from primary renal and metastatic sites in patients with metastatic renal cell carcinoma. Three of fifteen (20%) of informative renal carcinoma cell lines had loss of heterozygosity (LOH) in the RB gene (intron 20) detected by polymerase chain reaction analysis. Using restriction fragment length polymorphism (RFLP) analysis, 7 of 22 (32%) informative cell lines had LOH centromeric to the RB gene at the D13S1 locus. No LOH (0 of 7) was seen telomeric to the RB gene at the D13S2 locus. None of the 28 cell lines examined had decreased RB mRNA expression compared with short-term cultures of proximal renal tubular cells. Western blotting demonstrated phosphorylated and unphosphorylated forms of RB protein of expected molecular weight in all 41 cell lines (33 primary and 8 metastatic) examined. Twenty-nine primary cell lines and 6 metastatic cell lines all demonstrated normal immunohistochemical staining. Loss of RB immunohistochemical staining in paraffin-embedded tissue was detected in none of the primary tumors (0 of 30) or metastatic tumors (0 of 12). The absence of abnormalities of RB expression detected in these renal cell carcinomas suggests that abnormalities of the RB gene are not central to malignant transformation or progression in this tumor type; however, another tumor suppressor gene centromeric to the RB locus may be important in renal cell carcinogenesis.

The combined efforts of a number of investigators have led to the identification of the VHL gene, which appears to function as a tumor suppressor gene and is implicated in both sporadic and familial forms of RCC. These findings should increase our understanding of the molecular biology of this malignancy; however, there is much work to be done. Identification of the mechanism of inactivation of the VHL gene, as well as the structure and function of the VHL gene product, ultimately may provide clinicians with greater understanding of this malignancy as well as with methods for earlier diagnosis. The role of other tumor suppressor genes, such as p53, is incompletely understood. It is hoped that the techniques that have been applied to the study of RCC also will result in advances in our knowledge of other urologic malignancies.

We have developed a microdissection technique that allows for procurement and analysis of specific, minute cell populations from routine, 5-mu, formalin-fixed, paraffin-embedded histological tissue sections. Lesions < 1 mm in size can be specifically examined. Cells of interest are procured under direct microscopic visualization followed by a single-step DNA extraction and subsequent polymerase chain reaction. Amplification of DNA from selected cell populations was demonstrated by detecting a loss of heterozygosity (LOH) at the von Hippel-Lindau disease (VHL) gene in an atypical renal lesion and a renal cell carcinoma in a kidney of a VHL patient. Moreover, previously unrecognized LOH on the short arm of chromosome 3 (3p25-26) was detected in microdissected colorectal carcinoma cells in a non-VHL patient with sporadic colon carcinoma. This technique should prove useful in DNA studies of small lesions and cell populations. Furthermore, microscopic premalignant, in situ, and invasive lesions can be selectively examined.