Methioninase: a therapeutic for diseases related to altered methionine metabolism and transmethylation: cancer, heart disease, obesity, aging, and Parkinson's disease

Methionine metabolism and transmethylation are central to the metabolism and differentiation of all known cells. In enkaryotic organisms, methionine metabolism and transmethylation are of paramount importance in modification and regulation of proteins, lipids, and nucleic acids. The differential methylation of genes regulates their expression in the myriad of cells in eukaryotic organisms. Disruption and abnormalities in methionine metabolism and transmethylation seems to be associated with the major diseases of mankind, including cancer, heart disease, aging, obesity, and Parkinson's disease. In this review, we describe how aberrant and abnormal methionine metabolism and transmethylation are related to these major diseases. Most importantly, we review and hypothesize how the developing therapeutic recombination methioninase (rMETase) can be utilized to cure or prevent all of these diseases.

Conversion of highly malignant colon cancer from an aggressive to a controlled disease by oral administration of a metalloproteinase inhibitor

In this study, we describe the activity of CT1746, an orally-active synthetic MMP inhibitor that has a greater specificity for gelatinase A, gelatinase B and stromelysin than for interstitial collagenase and matrilysin, in a nude mouse model that better mimics the clinical development of human colon cancer. The model is constructed by surgical orthotopic implantation (SOI) of histologically-intact tissue of the metastatic human colon tumor cell line Co-3. Animals were gavaged with CT1746 twice a day at 100 mg/kg for 5 days after the SOI of Co-3 for 43 days. In this model CT1746 significantly prolonged the median survival time of the tumor-bearing animals from 51 to 78 days. Significant efficacy of CT1746 was observed on primary tumor growth (32% reduction in mean tumor area at day 36), total spread and metastasis (6/20 treated animals had no detectable spread and metastasis at autopsy compared to 100% incidence of secondaries in control groups). Efficacy of CT1746 could also be seen on reducing tumor spread and metastasis to individual organ sites such as the abdominal wall, cecum and lymph nodes compared to vehicle and untreated controls. We conclude that chronic administration of a peptidomimetic MMP inhibitor via the oral route is feasible and results in inhibition of solid tumor growth, spread and metastasis with increase in survival in this model of human cancer, thus converting aggressive cancer to a more controlled indolent disease.

Topical liposome delivery of molecules to hair follicles in mice

The hair cycle consisting of growing and resting phases, is subject to widespread disease such as androgenic alopecia or loss of pigment which are in need of effective, targeted therapeutics. In order to develop a hair-follicle delivery system we demonstrate here that phosphatidylcholine liposomes entrapping either the fluorescent dye calcein or the pigment melanin can deliver these molecules into the hair follicle and hair shafts of mice when applied topically. Liposomal delivery of these molecules is time dependent. Negligible amounts of delivered molecules enter the dermis, epidermis or blood stream thereby demonstrating the enrichment of follicle delivery. Naked calcein and melanin are trapped in the stratum corneum and are unable to enter the follicle. The potential of the hair-follicle liposome delivery system for therapeutic use for hair disease is discussed.

Interleukin-6 production in primary histoculture by normal human kidney and renal tumor tissues

Interleukin-6 (IL-6) is a multifunctional cytokine with many biologic activities in vitro, including synergistic or antagonistic actions with one or more other cytokines. The role and induction parameters of IL-6 in renal cell carcinoma (RCC) are not fully understood. To understand the ability of RCC to produce IL-6, we determined the IL-6 concentration in the supernatant of histocultured human normal kidney, RCC, renal Wilms' tumor and renal oncocytoma. From these studies, we conclude that the kidney is one of the main sources of IL-6. Normal renal cortical tissues and renal tumors can produce IL-6 in histoculture without stimulation. Thus histoculture supports the long-term production of IL-6, potentially allowing many important studies of this cytokine in the normal and malignant kidney.

Efficacy of the platinum analog [Pt(cis-dach)(DPPE)-2NO3] on histocultured human patient bladder tumors and cancer cell lines

Cisplatinum is currently used as a front line agent in many important tumors, but its dose-limiting nephrotoxicity prevents potential efficacy. There is therefore great interest in developing new platinum agents that have less toxicity. We have synthesized new platinum analogues containing DACH as a carrier ligand and DPPE as a leaving group. Previously we showed that these new platinum complexes have much less nephrotoxicity than cisplatinum. In the present study, the efficacy of one new platinum complex was evaluated with human patient bladder tumor specimens in three-dimensional histoculture as well as with monolayer cultures of cancer cell lines. The efficacy end points used were glucose consumption and thymidine incorporation on the histocultured specimens and MTT reduction on monolayer cell cultures. Our results showed that the new platinum complex was more effective at high concentration (10(-3) M) but less effective at low concentration (10(-4) M) compared to cisplatinum on histocultured bladder tumor specimens. The compound demonstrated higher efficacy than cisplatinum on P-388, and L-1210 leukemic cell lines. The new analog demonstrated similar efficacy to cisplatinum on the MKN-45 human stomach cancer cell line. The PC-14 human lung cancer cell line, MH1C1 rat hepatoma cell line, NIH-OV3, SKOV-3 ovarian cancer cell lines were as sensitive to the new analog as to cisplatinum at high concentrations of the new platinum analogue. The cisplatinum-resistant M-14 melanoma cell line was not sensitive to either the new analog or cisplatinum. Based on these results, this novel platinum compound appears to be a valuable lead compound with high efficacy and low nephrotoxicity.

Methionine starvation modulates the efficacy of cisplatin on human breast cancer in nude mice

There are few agents with activity against metastatic breast cancer. We therefore exploited the elevated methionine dependence of tumors to develop a selective and effective therapy against metastatic breast and other cancers. Methionine starvation leads to depleted methionine levels in cells, modifies methylation reactions, lowers glutathione levels and alters folate distribution and leads to a tumor-selective cell cycle arrest in late-S/G2. These effects present the opportunity for methionine depletion to modulate the efficacy of a number of different classes of chemotherapeutic drugs. This report demonstrates that methionine depletion can strongly modulate the efficacy of cisplatin against the MX-t human breast carcinoma cell line when grown in nude mice. The tumor-bearing nude mice were subjected to a methionine-free diet and were additionally treated with cisplatin i.p. at one mg/kg once a week for 3 weeks. The MX-t tumor was relatively resistant to both methionine starvation and cisplatin alone but was very sensitive to the combination of methionine starvation and cisplatin with a 32.1% T/C ratio. The intratumoral platinum concentration was higher in combination with methionine starvation than cisplatin alone, possibly accounting for at least part of the modulating effect of methionine depletion. Future studies will focus on methionine depletion via the enzyme methioninase to modulate cisplatin as well as other classes of chemotherapeutic agents in order to develop a new approach to the treatment of cancer.

Serum methionine depletion without side effects by methioninase in metastatic breast cancer patients

The growth dependence of human tumors on elevated levels of methionine has been shown in preclinical in vitro and in vivo studies to be a frequently occurring, highly effective, tumor-selective therapeutic target. High purity endotoxin-free methioninase was produced from Pseudomonas putida in order to develop anti-methionine chemotherapy targeting of human tumors. A pilot Phase I clinical trial has been initiated in order to determine methioninase toxicity, the pharmacokinetics of methioninase and methionine-depletion and maximum tolerated dose. A two hour i.v. infusion of 5,000 units (0.4 g) and 10,000 units (0.8 g) and a ten hour i.v. infusion of 20,000 units (1.6 g) of methioninase was administered to patient-1, patient-2, and patient-3, respectively. All patients had advanced breast cancer. Blood and urine samples were obtained at frequent intervals between 0 and 24 hours. The toxicity evaluations were carried out according to FDA criteria. Pharmacokinetics data were obtained for both methioninase and methionine levels in the serum. No acute clinical toxicity was observed for all the toxicity criteria measured in patient-1, patient-2 and patient-3. The depletion of serum methionine started within 30 minutes of the infusion, and was maintained for 4 hours after the infusion was completed in patient-1 and patient-2. The lowest serum methionine levels were 35% and 19% of the pretreatment level, respectively, in patient-1 and patient-2. Patient-3 received a ten hour i.v. infusion of 20,000 units of methioninase without any signs of side effects. Patient-3 maintained serum levels of methioninase as high as 50% of the maximum level for a subsequent 6 hours after infusion. Methionine was depleted over 200-fold from 23.1 microM to 0.1 microM by the 10-hour infusion of patient-3. No clinical toxicity was observed whatsoever in all the toxicity criteria measured in patient-3. The results of the methioninase pilot Phase 1 clinical trial suggested that i.v. infusion of the methioninase is safe and effectively depletes serum methionine without any signs of side effects. Clinical studies are continuing to determine the maximum length of time complete serum methionine depletion can be tolerated.

Anticancer efficacy of methioninase in vivo

Therapeutics that are selective for cancer would have a high potential for efficacy. We have previously shown that the metabolic defect of enhanced methionine dependence is a broad cancer-selective target. Methionine depletion can completely arrest the growth of methionine-dependent tumor cells in vivo with a reversible pre-mitosis cell-cycle block. Dietary methionine depletion can partially arrest the growth of methionine-dependent rodent tumors in vivo. This report demonstrates that methioninase isolated from Pseudomonas putida can arrest rodent and human tumors in nude mice with no apparent toxic side effects. Methioninase injected i.p. arrested the growth of the Yoshida sarcoma in nude mice and greatly slowed the growth of the H460 human non-small-cell-lung carcinoma in nude mice. The effectiveness of methioninase against H460 was in contrast to 5-fluorouracil and vincristine, which were inactive against this tumor. The activity of the administered methioninase did not cause weight loss for up to 10 days treatment at 40-120 units/day indicating the possibility of low toxicity. In contrast, vincristine was highly toxic despite its ineffectiveness. Methioninase also induced a tumor-specific late cell-cycle block. The tumor-selective late cell-cycle block induced by methioninase should be able to be exploited to enhance the tumor specificity of antimitotic drugs and other agents in future experiments. Thus methioninase is a highly effective antitumor agent with a new tumor-selective mode of action with minimal toxicity, demonstrating potential clinical effectiveness against solid tumors.

Interferon gamma is highly effective against orthotopically-implanted human pleural adenocarcinoma in nude mice

The efficacy of recombinant human gamma interferon (rh IFN-gamma) was evaluated for the treatment of human pleural adenocarcinoma in a patient-like nude mice model which is constructed by surgical orthotopic implantation (SOI) of histologically-intact human tumor tissue. The human non-small-cell lung cancer cell line H-460 was used for the study. Gamma interferon was tested in three different dosages (25,000 U, 50,000 U and 100,000 U) versus an untreated control through i.p. injection twice a day for five days, which was started 48 hours after SOI; The results showed that IFN-gamma can prolong the survival time of the tumor-bearing animals. The symptoms and signs of hypoxia such as restricted physical activity and cyanosis due to primary tumor growth in the thoracic cavity as well as cachexia developed much earlier in the control than in the IFN-gamma-treated mice. The mice in the control group had succumbed by day-23 after tumor implantation, however at that time 67% of the mice in the 100,000 U-treated group, 15% of the mice in the 50,000 U-treated group, and 16% of the mice in the 25,000 U-treated group were still alive. The orthotopically-transplanted tumor grew rapidly and metastasized to the lung and liver in the untreated control. In the IFN-gamma-treated groups both primary tumor growth and metastasis were reduced, probably accounting for the increased survival rate. The results demonstrated dose-dependent efficacy of IFN-gamma in suppressing symptomology, primary tumor growth, invasiveness and metastasis of the human lung cancer cell line H 460, and increased survival of the tumor-bearing animals. These results suggest clinical trials of IFN-gamma should begin for treatment of pleural adenocarcinoma for which there is no current effective therapy.

Methionine depletion modulates the antitumor and antimetastatic efficacy of ethionine

The elevated methionine requirement for the growth of tumors, termed methionine dependence, is a potentially highly effective therapeutic target. To attack this target we are developing anti-methionine chemotherapy. In this study of anti-methionine chemotherapy we have observed that the methionine analog ethionine is synergistic with methionine depletion in arresting the growth of the Yoshida sarcoma both in vitro and when transplanted to nude mice. In contrast, ethionine in vitro in a methionine-containing medium is not effective against Yoshida sarcoma cells. Similarly, ethionine administered along with a methionine-containing diet is ineffective against the Yoshida sarcoma growing in nude mice. A methionine-depleted diet alone is only partially effective against tumor growth. The Yoshida sarcoma gave rise to metastases in 75% of the- organs observed in the mice on the methionine-containing diet, and 43 % of the organs in the mice on the methionine-free diet. In striking contrast, no metastases were observed in the ethionine-treated animals on the methionine-free diet. Anti-methionine chemotherapy consisting of dietary methionine depletion and ethionine administration caused an initial weight loss but the animals weight stabilized resulting in no animal deaths. The synergism of ethionine and methionine depletion is markedly similar in vitro and in vivo suggesting the observed efficacy is due to the specific anti-methionine targeting. Thus methionine depletion highly potentiates the anti-tumor and anti-metastatic effectiveness of ethionine suggesting that anti-methionine chemotherapy consisting of methionine depletion as a modulator of methionine analogs holds great promise as a new, tumor-selective therapeutic approach.

IL-2 gene therapy of advanced lung cancer patients

We report here Phase I clinical-trial studies of retroviral-mediated interleukin-2 (IL-2) gene transfer to tumor-infiltrating lymphocytes that are re-infused to advanced lung cancer patients with pleural effusions. Ten lung cancer patients with malignant pleural effusions for whom all conventional therapy had failed were included in this Phase I protocol. Tumor infiltrating lymphocytes (TIL) from the patients were exposed to the retroviral plasmid pL(IL-2)SN containing the human IL-2 gene. Approximately 1-6 x 10(10) TIL cells transfected with IL-2 were re-infused into the chest cavity of each patient. The toxicity of this treatment with TIL/IL-2 gene therapy in these patients was minimal with transient slight fever of approximately 37.5. Pleural effusions did not re-accumulate for at least 4 weeks in six of ten patients. One patient was observed to have not only the resolution of the pleural effusions, but in addition the size of the original tumor decreased as seen by CT. The clinical results indicate this method of cancer gene therapy is safe and possibly efficacious against pleural effusions due to advanced lung cancer.

Attitudes and practices of primary care physicians for prostate cancer screening

Prostate cancer screening with digital rectal examination (DRE) and prostate-specific antigen (PSA) is recommended by several professional organizations. Our objective was to assess the prostate cancer screening practices and attitudes reported by primary care physicians. We randomly surveyed 454 Arizona primary care physicians, subsequently excluding 124 ineligible subjects. Overall, 141 of 329 eligible physicians completed the survey (42.9%). Survey data included physician demographics, practice characteristics, screening and follow-up strategies, and attitudes toward screening. One hundred thirty-one physicians (93%) reported screening asymptomatic men with DRE or PSA. Respondents generally agreed that screening tests were accurate and that early detection was beneficial. Screening began at an average patient age of 45 years, though 7.8% of respondents began screening men younger than 40 years and 7.0% began screening men older than 50 years. PSA levels ranging from 3.9 to 40 ng/mL were considered abnormal, and 11.6% of respondents used a cutpoint higher than 10 ng/mL. Primary care physicians report a high rate of screening for prostate cancer and consider PSA and DRE accurate and useful tests. Screening practices, however, varied considerably between physicians. The screening of younger men reported by practitioners would tend to increase the rate of false-positive tests, while using a high cutpoint for PSA and delaying screening beyond age 50 years would decrease the chance for early detection. These screening practices may increase health care costs without necessarily leading to improved health outcomes. Medical Subject Headings (MeSH): prostatic neoplasms, prostate-specific antigen, primary health care, screening.

Calcium decreases and parathyroid hormone increases in serum of periparturient mares

Changes in serum concentrations of Ca and parathyroid hormone (PTH) may develop in periparturient mares, may be influenced by dietary Ca, and may be associated with changes in Ca concentration of mammary secretion. Milk and blood samples were taken from eight mares on Farm A and eight on Farm B for 10 d before parturition and from four mares on each farm for 5 d postpartum. Milk Ca was measured by two commercial tests. Serum samples were analyzed for PTH and total Ca in 16 mares and for ionized Ca in six (Farm A). Parturition was induced in eight mares on Farm A and four on Farm B; no significant difference in serum Ca or PTH was found between mares with induced and spontaneous foaling. Mean serum total Ca decreased from 12.5 mg/dL to a nadir of 11 mg/dL on d 2 postpartum, and mean PTH increased from 46 pg/mL to a peak of 186 pg/mL on d 2 postpartum. Serum total Ca concentrations were lower and serum PTH concentrations were higher in Farm A mares than in Farm B mares, probably reflecting dietary Ca (.35% of DM on Farm A and .55% on Farm B). The serum PTH peak and Ca nadir occurred on d 2 postpartum, 1 d later than reported previously in dairy cows. Milk Ca concentration increased progressively from 7 d before parturition; this increase preceded, so was not dependent on, prepartal changes in serum Ca and PTH.

Depth-targeted efficient gene delivery and expression in the skin by pulsed electric fields: an approach to gene therapy of skin aging and other diseases

The ability to target genes to the various layers, cell types, and appendages of the skin could be used to correct disorders, including those of aging such as wrinkling, as well as utilize specific cell types for production molecules useful elsewhere in the body. However, the stratum corneum acts as a significant physical barrier to gene transfer into the skin. In this report we describe the ability to target and express the lacZ reporter gene to various depths of the dermis region in hairless mice. Skin-depth targeting is achieved by varying pulsed electrical fields and subsequent pressure from caliper-type electrodes on topically applied naked lacZ gene constructs. With electric pulses and extended pressure, the maximum depth of lacZ expression in the dermis and transfected cells was achieved at 370 micron and 457 cells/mm2, respectively. Gene expression was observed only the hair follicles in the case of the control.

A clinical nude mouse metastatic model for highly malignant human pancreatic cancer

Pancreatic cancer is a highly aggressive and treatment-refractory cancer. A clinically-relevant animal model is necessary to develop therapy for metastatic pancreatic cancer. In this study we evaluated the efficacy of mitomycin C (MMC) and 5-FU against the human pancreatic adenocarcinoma cell line PAN-12 in an orthotopic human metastatic pancreatic cancer nude mice model. The model is constructed by surgical orthotopic implantation (SOI) of histologically intact tumor tissue in the tail portion of the pancreas near the spleen. PAN-12 grew very aggressively in the control group of nude mice with extensive local invasion and distant metastasis to various organs with a propensity for the lung but to other organs as well, including the liver, kidney and regional and distant lymph nodes. In a striking effect none of the mice in the MMC-treated group developed tumor. Although mice in the 5-FU treated group survived statistically significantly longer than those in the untreated control, the overall incidence of metastasis in these mice was equivalent to those in the control. However no liver or kidney metastases were found in the 5-FU treated animals perhaps accounting in part for their longer survival. This "clinical" nude mouse model of highly metastatic pancreatic cancer can now be used to discover new effective agents for this disease.

Clinical course of human epithelial-type malignant pleural mesothelioma replicated in an orthotopic-transplant nude mouse model

Malignant pleural mesothelioma is an aggressive tumor that is essentially unresponsive to standard medical and surgical therapies. Little is actually known about its biologic response to therapeutic interventions, in part because of a lack of a "patient-like" animal tumor model. Most experimental models thus far have been derived from inhalation or inoculation of asbestos fibers into animal subjects or by subcutaneous transplantation of human mesothelial cell lines into nude mice. These models are not representative of clinical malignant pleural mesothelioma. In this report, an animal model of human pleural malignant mesothelioma obtained by orthotopic transplantation of intact pleural tumor tissue into athymic nude mice is described. Pleural tumor obtained by thoracolscopy from a patient with epithelial-type malignant pleural mesothelioma was implanted as intact tissue by surgical orthotopic implantation (SOI) into the right pleural cavity of nude mice. Animals were sacrificed when moribund or 6 months after implantation. Tumor growth and regional spread in the mice evaluated at post-mortem examination mimicked the clinical pattern of progression of human disease. Histologic findings and the immunohistochemical profile were similar to those demonstrated on examination of thoracoscopic parietal pleural biopsy specimens and post-mortem examination of the original patient's tumor. This "patient-like" nude mouse model of epithelial-type malignant pleural mesothelioma, phenotypically similar to the original human tumor, should facilitate future investigation of tumorigenesis and metastatic potential of this neoplasm. The model should serve as a basis for assessing the impact of experimental and existing therapy on malignant mesothelioma.

"Decadose" effects of cisplatin on squamous cell carcinoma of the upper aerodigestive tract. I. Histoculture experiments

There is substantial laboratory and clinical evidence that solid tumors rapidly acquire cellular resistance to cisplatin. Experiments with human carcinoma cell lines and clonogenic assays indicate that resistance is usually mild to moderate and can be circumvented with higher concentrations of drug. The purpose of this investigation was to test this hypothesis with a histoculture assay of human upper aerodigestive tract (UADT) carcinomas. Using a sponge-gel supported histoculture, 43 tumor specimens from patients with squamous cell carcinoma (SCC) of the UADT were grown and exposed to cisplatin. Growth inhibition by the drug, in concentrations equivalent to peak therapeutic doses (1.5 micrograms/mL) and concentrations 10 and 25 times greater (15 and 37.5 micrograms/mL), were measured in specimens from patients with previously untreated and recurrent lesions. In vitro, the overall rate of sensitivity of the tumor samples to cisplatin concentrations of 1.5, 15, and 37.5 micrograms/mL were 22%, 62%, and 83%, respectively. In patients with previously untreated disease, the respective rates were 25.9%, 63.3%, and 79.3%, as compared with 10.0%, 55.6%, and 85.6%, respectively, for patients with recurrent disease. The response difference between cisplatin concentrations of 1.5 and 15 micrograms/mL was statistically significant. The "decadose" effect of cisplatin on growth inhibition was 2.44-fold for untreated lesions and 5.56-fold for recurrent tumors. The results indicate that resistance to standard doses of cisplatin by SCC of the UADT can be substantially overcome with a decadose (standard dose x 10) increase and is more pronounced in tumors from patients with recurrent disease. Progress toward improving survival of patients may be possible by incorporating decadose cisplatin therapy into a multimodality treatment plan.

Liver colonization competence governs colon cancer metastasis

Tumors that metastasize do so to preferred target organs. To explain this apparent specificity, Paget, > 100 years ago, formulated his seed and soil hypothesis; i.e., the cells from a given tumor would "seed'' only favorable "soil'' offered by certain groups. The hypothesis implies that cancer cells must find a suitable "soil'' in a target organ--i.e., one that supports colonization--for metastasis to occur. We demonstrate in this report that ability of human colon cancer cells to colonize liver tissue governs whether a particular colon cancer is metastatic. In the model used in this study, human colon tumors are transplanted into the nude mouse colon as intact tissue blocks by surgical orthotopic implantation. These implanted tumors closely simulate the metastatic behavior of the original human patient tumor and are clearly metastatic or nonmetastatic to the liver. Both classes of tumors were equally invasive locally into tissues and blood vessels. However, the cells from each class of tumor behave very differently when directly injected into nude mouse livers. Only cells from metastasizing tumors are competent to colonize after direct intrahepatic injection. Also, tissue blocks from metastatic tumors af fixed directly to the liver resulted in colonization, whereas no colonization resulted from nonmetastatic tumor tissue blocks even though some growth occurred within the tissue block itself. Thus, local invasion (injection) and even adhesion to the metastatic target organ (blocks) are not sufficient for metastasis. The results suggest that the ability to colonize the liver is the governing step in the metastasis of human colon cancer.

Plummer-Vinson syndrome. A case report and literature review

The Plummer-Vinson syndrome is characterized by dysphagia, iron-deficiency anemia, and esophageal webs. The webs are best diagnosed by cineradiography. Iron repletion often improves the dysphagia, although some patients require esophageal dilatation or bougienage. The syndrome is associated with an increased incidence of postcricoid carcinoma, and surveillance endoscopy is recommended.

Rapid rise and subsequent decline in prostate cancer incidence rates for New Mexico, 1989-1993

Beginning in the late 1980s, a large increase in incidence rates for prostate cancer occurred in association with increased prostate-specific antigen (PSA) screening. In New Mexico, the increased screening was associated with earlier detection of cancers and decreased prostate cancer mortality, suggesting that PSA screening may be effective. PSA screening has become a controversial topic of public debate, and anecdotal reports from physicians indicated that prostate cancer screening practice patterns were changing in New Mexico. To assess whether PSA-associated trends in prostate cancer incidence were continuing, we examined incidence rates from 1989 to 1993 among men in New Mexico. From 1989 to 1992, age-adjusted rates increased substantially for non-Hispanic whites (77%), Hispanics (50%), and American Indians (27%). Although rates increased for all stages combined, incidence rates decreased for distant-stage disease, especially for non-Hispanic whites, indicating a continuing trend toward earlier detection. In 1993, incidence rates unexpectedly decreased from 203 to 158/100,000 in non-Hispanic whites, largely as a result of changes in rates in men over age 65 years. Although incidence rates decreased, the trend toward earlier detection was maintained for non-Hispanic whites. In contrast, among Hispanic and American Indians, rates did not change substantially between 1992 and 1993. Because the epidemic in prostate cancer was associated with increased PSA screening, it is likely that the trends for non-Hispanic whites are also related to PSA screening. We suggest that the decrease in rates and the continued stage shift are consistent with repeated screening of men in the population at risk.