Brostallicin versus doxorubicin as first-line chemotherapy in patients with advanced or metastatic soft tissue sarcoma: an European Organisation for Research and Treatment of Cancer Soft Tissue and Bone Sarcoma Group randomised phase II and pharmacogenetic study.

AIM: Brostallicin is a DNA minor groove binder that has shown activity in patients with soft tissue sarcoma (STS) failing first-line therapy. The present study assessed the safety and efficacy of first-line brostallicin in patients with advanced or metastatic STS >60 years or not fit enough to receive combination chemotherapy. A prospective explorative pharmacogenetic analysis was undertaken in parallel. METHODS: Patients were randomised in a 2:1 ratio between IV brostallicin 10mg/m(2) and doxorubicin 75 mg/m(2) once every 3 weeks for a maximum of six cycles. Disease stabilisation at 26 weeks (primary end-point) was considered a 'success'. Further testing of brostallicin was warranted if ≥ 35 'successes' were observed in the first 72 eligible patients treated with brostallicin. In addition, patients were genotyped for glutathione S transferase (GST) polymorphisms. RESULTS: One hundred and eighteen patients were included (79 brostallicin and 39 doxorubicin). Brostallicin was well tolerated in comparison to doxorubicin with less grade 3-4 neutropenia (67% versus 95%), grade 2-3 systolic dysfunction (0% versus 11%), alopecia (17% versus 61%) and grade 2-3 mucositis (0% versus 18%). For brostallicin versus doxorubicin, 'successes' were observed in 5/77 versus 10/36, progression free survival at 1 year was 6.5% versus 15.6%, objective response rate was 3.9% versus 22.2% and overall survival at 1 year was 50.5% versus 57.9%, respectively. Only GSTA1 genotype was significantly associated with success rate of doxorubicin treatment. CONCLUSION: Brostallicin cannot be recommended at this dose and schedule in this patient population as first-line therapy. GSTA1 genotype may be predictive for doxorubicin efficacy but warrants further study.

Liquid chromatography-mass spectrometry assay of a thiadiazole derivative in mice: application to pharmacokinetic studies.

Modern atmospheric pressure ionization (API) ion-trap mass spectrometry in connection with fast chromatographic separations using a short narrow-bore C8 column was developed to determine 5-phenyl-3-thioureido-1,2,4-thiadiazole (301029), a novel virus inhibitor in serum. Both 301029 and an internal standard (I.S.) were separated from serum samples by acetonitrile deproteinization and extraction without time-consuming reconstitution. The chromatographic separation was achieved on a C8 reversed-phase narrow-bore column using acetonitrile-water-acetic acid (90:10:0.01, v/v/v) as a mobile phase. The mass spectrometric analysis was performed by atmospheric pressure chemical ionization (APCI) mode with positive ion detection. Single ion monitoring (SIM) scan mode of m/z 237 and 158 was used to quantitatively determine 301029 and I.S., respectively. The low limit of quantitation was 25 ng/ml. The assay exhibited a linear range of 25-2500 ng/ml. Recovery from serum proved to be 100-113%. The precision (C.V.) and accuracy (RE) of the method were 2-12% and 94-112%, respectively. The present method was applied to determine the pharmacokinetic parameters of 301029 following oral administration of the agent to mice at 5 g/kg. The results revealed that the elimination half-life of 301029 was 413 min and the area under serum concentration-time curve was 354 microg/ml/min.

Antitumor activity of MGI 114 (6-hydroxymethylacylfulvene, HMAF), a semisynthetic derivative of illudin S, against adult and pediatric human tumor colony-forming units.

MGI 114 (6-hydroxymethylacylfulvene, HMAF) is a novel semisynthetic antitumor compound derived from the sesquiterpene mushroom toxin illudin S. Although illudins did not demonstrate significant activity as antiproliferative agents in tumor-bearing animals, several properties including its potent inhibition of DNA synthesis and a unique interaction with DNA led to a structure-activity-based synthetic effort to obtain analogs with improved therapeutic potential. MGI 114 was selected for further development based on its antitumor activity in numerous preclinical tests. MGI 114 was evaluated against adult and pediatric human tumors taken directly from cancer patients and cultured in a human tumor colony-forming assay (HTCFA) to assess the antitumor spectra, concentration-response relationship, schedule dependence and activity of this agent against tumors considered resistant to conventional anticancer drugs. Human tumor colony-forming units were treated with HMAF at concentrations of 0.001, 0.01, 0.1 and 1 microg/ml, both as a 1 h exposure and as a continuous 14 day exposure. A response was scored if there was 50% or less colony survival. In vitro response rates in the range of 50-80% were observed against tumor colony-forming units originating from carcinomas of the colon, kidney, breast, lung cancer, ovary and melanoma. MGI 114 also demonstrated antitumor activity against neuroblastoma colony-forming units. Antitumor activity was not influenced by exposure time as demonstrated by the similar responses rates obtained with the 1 h and continuous exposure at all concentrations tested. However, there was a significant positive concentration-response relationship to both exposure duration with responses increasing from below 10% at the lowest concentration to over 70% at the highest concentration, except for the pediatric tumors on the 1 h exposure for which this relationship was less apparent. At the higher concentration tested, MGI 114 displayed substantial antiproliferative effects in the range of 70% against tumor specimens resistant to classic cytotoxic agents including irinotecan, paclitaxel, 5-fluorouracil, cisplatin, doxorubicin and cyclophosphamide. These results demonstrate that MGI 114 exhibits a broad spectrum of antitumor activity against both adult and pediatric primary tumor colony-forming units in a concentration-dependent manner both at short and prolonged exposure duration. The substantial in vitro activity of MGI 114 at concentrations achievable in clinical trials, together with its activity against tumors resistant to classic standard cytotoxic drugs, justifies the further clinical evaluation of this unique agent.

Comparison of DX-8951f and topotecan effects on tumor colony formation from freshly explanted adult and pediatric human tumor cells.

DX-8951f, which shows great therapeutic potential, was tested in the human tumor cloning system in adult and pediatric tumor types against which topotecan has been active. In 47 tumors from adults, DX-8951f had definite cytotoxic activity in a concentration-dependent manner with both 1 h and continuous exposures. Topotecan was minimally effective using a 1 h exposure and showed concentration-dependent inhibition with continuous exposure. In head-to-head comparisons at 1 h exposure against adult tumors, DX-8951f was significantly more effective at 0.1 and 1.0 microg/ml than topotecan. In head-to-head comparisons (continuous exposure), 1.0 microg/ml DX-8951f was more effective than topotecan at 1.0 microg/ml in adult tumors, including three of four head and neck, one of two kidney, two of five liver, six of 10 non-small cell lung, five of eight ovarian, four of eight prostate tumors, and in single specimens of breast, mesothelioma, colon and small cell lung tumors. With continuous exposure, DX-8951f and topotecan were equally effective at equimolar concentrations. The maximum tolerated dose for DX-8951f is 3 times that of topotecan, so higher doses of DX-8951f could be administered to patients. DX-8951f is a promising new antineoplastic agent with significant activity against tumors taken directly from patients.

Comparative activity of the cyclopropylpyrroloindole compounds adozelesin, bizelesin and carzelesin in a human tumor colony-forming assay.

Adozelesin, bizelesin and carzelesin are synthetic cyclopropylpyrroloindole (CPI) analogs, a class of potent antineoplastic agents modeled on the antitumor antibiotic CC-1065, that specifically bind to the minor groove of DNA and preferentially alkylate AT-rich regions. These compounds were evaluated against fresh human tumors in a human tumor colony-forming assay (HTCFA) to assess and to compare their relative antitumor spectra, concentration-response relationships and schedule-dependence. Human tumor colony-forming units were treated with adozelesin and bizelesin at concentrations of 0.02, 0.1 and 0.5 ng/ml as a continuous exposure for 14 days, and to 0.2, 1.0 and 5.0 ng/ml as a 1 h exposure. Carzelesin concentrations were 0.04, 0.2 and 1 ng/ml as a continuous exposure, and 0.6, 3.0 and 15.0 ng/ml as a 1 h exposure. A response was scored if there was 50% or less colony survival. The three analogs had similar antitumor activity against colon carcinoma, kidney carcinoma and melanoma colony-forming units. Adozelesin also displayed activity against both breast and non-small cell lung carcinoma colony-forming units, and carzelesin was active against ovarian carcinoma colony-forming units. Significantly positive concentration-response relationships were apparent with all three agents. Responses increased from below 15% at the lowest concentration to above 45% at the highest concentration for the three drugs on all schedules (p < 0.01). At the highest concentration, the overall response rate was significantly higher (p < 0.01) with carzelesin on the continuous schedule (71%) compared to the 1 h schedule (46%). However, overall response rates for adozelesin and bizelesin were similar on both schedules (1 h/continuous: adozelesin, 67/58%; bizelesin, 49/44%), indicating that adozelesin and bizelesin are less schedule dependent than carzelesin in the HTCFA. These results demonstrate that the CPIs have broad-spectrum activity against human tumor colony-forming units in the HTCFA at very low concentrations, as well as differences with regard to schedule dependence which may help guide the optimal clinical development of these agents.

Significant activity of a novel cytotoxic agent, LY295501, against a wide range of tumors in the human tumor cloning system.

The diarylsulfonylureas (DSUs) are a novel class of cytotoxic agents with high potential for activity. LY295501 is one of the most active DSUs. In this study, we evaluated the cytotoxicity of LY295501 utilizing the human tumor cloning assay. LY295501 was tested at 10, 50 and 100 microg/ml using either 1 h or continuous exposure schedules. The majority of common solid tumors were evaluated including breast, colorectal, non-small cell lung and ovarian carcinomas. LY295501 demonstrated significant activity against all tumor types tested. Antitumor activity was noted after either 1 h or continuous exposure schedules at all concentrations tested. A concentration-response relationship was noted, with increasing concentrations of LY295501 leading to more cytotoxicity. Cytotoxicity, on the continuous exposure schedule, was noted in 38% of tumors exposed to LY295501 at 10 microg/ml, 58% of tumors exposed at 50 microg/ml (p=0.002 for 10 versus 50 microg/ml) and 72% of tumors exposed at 100 microg/ml (p=0.008 for 50 versus 100 microg/ml). In addition, more cytotoxicity was observed on the continuous exposure schedule compared to the 1 h schedule at all concentrations tested (p<0.01). The substantial activity of LY295501 in the human tumor cloning assay coupled with its clinical activity in phase I studies supports further clinical development of this agent.

Activity of MKT 077, a rhodacyanine dye, against human tumor colony-forming units.

MKT 077 is related to rhodamine 123 dye and demonstrates preferential accumulation in the mitochondria of cancer cells compared to normal cells. This difference in retention between cancer and normal cells led to the finding that MKT 077 selectively inhibits the growth of cancer cells in vitro. To define the preclinical activity profile of MKT 077, the compound was tested in vivo against a large variety of human tumors utilizing the human tumor-cloning assay. MKT 077 was studied using a sequential 2 h exposure separated by 24 h (2-24-2 h) and a 24 h exposure at final concentrations of 0.1, 0.2, 1.0, 2.0, 10.0 and 20.0 microg/ml. MKT 077 was also studied using continuous exposure at final concentrations of 0.1, 1.0 and 10 microg/ml. A decrease in tumor colony formation was considered significant if survival of colonies treated with MKT 077 was 50% or less compared to untreated controls. A total of 149 specimens was treated with MKT 077 with 51, 58 and 34 evaluable specimens with the 2-24-2 h, the 24 h and the continuous exposure, respectively. The results of the present study suggest a positive relationship between concentration and response. No relationship between exposure schedule and activity was observed. Inhibitory effects were obtained against multiple tumor types. High cytotoxic activity was obtained against breast, ovary, endometrial, colon and non-small cell lung cancer with concentrations of 2 microg/ml or above. In conclusion, the broad spectrum of cytotoxicity of MKT 077 in the human tumor-cloning assay and the unique mechanism of action of MKT 077 encourage additional preclinical and clinical studies with this compound and other rhodacyanine dyes.

Phase I trial of 9-aminocamptothecin in children with refractory solid tumors: a Pediatric Oncology Group study.

PURPOSE: A phase I trial of 9-aminocamptothecin (9-AC) was performed in children with solid tumors to establish the dose-limiting toxicity (DLT), maximum-tolerated dose (MTD), and the pharmacokinetic profile in children and to document any evidence of activity. PATIENTS AND METHODS: A 72-hour infusion of 9-AC dimethylacetamide formulation was administered every 21 days to 23 patients younger than 21 years of age with malignant tumors refractory to conventional therapy. Doses ranged from 36 to 62 microg/m2 per hour. Pharmacokinetics were to be performed in at least three patients per dose level. The first course was used to determine the DLT and MTD. RESULTS: Nineteen patients on four dose levels were assessable for toxicities. At 62 microg/m2 per hour, three patients experienced dose-limiting neutropenia and one patient experienced dose-limiting thrombocytopenia. Pharmacokinetics were performed on 15 patients (nine patients had complete sets of plasma sampling performed). The pharmacokinetics of both lactone and total 9-AC were highly variable. The percentage of 9-AC lactone at steady-state was 10.8% +/- 3.6%. Total 9-AC and its lactone form had a terminal half-life of 8.1 +/- 3.8 and 7.1 +/- 3.9 hours, respectively, and a volume of distribution at steady-state (Vdss) of 21.2 +/- 13.3 L/m2 and 135.3 +/- 52.5 L/m2, respectively. Hepatic metabolism and biliary transport had an important role in 9-AC disposition. CONCLUSION: The recommended phase II dose of 9-AC administered as a 72-hour infusion every 21 days to children with solid tumors is 52 microg/m2 per hour. Neutropenia and thrombocytopenia were dose limiting.

Hepatocellular carcinoma in children associated with Gardner syndrome or familial adenomatous polyposis.

PURPOSE: Gardner syndrome, a variant of familial adenomatous polyposis, is characterized by colonic polyps that undergo malignant change and benign and malignant extracolonic lesions. Tumors frequently associated with Gardner syndrome include carcinoma of the ampulla of Vater, papillary carcinoma of the thyroid, and, in children, hepatoblastoma. The childhood malignancies often precede the appearance of other manifestations by several years. PATIENTS AND METHODS: Two patients are described. Gardner syndrome was diagnosed in a 15-year-old girl with fibrolamellar hepatocellular carcinoma after desmoid tumors and colonic polyposis developed. Classic hepatocellular carcinoma was also diagnosed in a 9 1/2-year-old boy with familial adenomatous polyposis. RESULTS: In patient 1, the diagnosis of fibrolamellar hepatocellular carcinoma preceded the diagnosis of Gardner syndrome by almost 2 years. The diagnosis was confirmed by identifying a germline mutation of the adenomatous polyposis coli (APC) gene. This is the first patient reported with fibrolamellar hepatocellular carcinoma associated with Gardner syndrome. Patient 2 had a strong family history of familial adenomatous polyposis but no manifestations of Gardner syndrome. He was not tested for the APC mutation. The current literature and previously reported cases of hepatocellular carcinoma in patients with Gardner syndrome or familial adenomatous polyposis are reviewed. CONCLUSIONS: Because hepatocellular carcinoma is uncommon in the pediatric and adolescent population, it is important to consider the possibility of Gardner syndrome or familial adenomatous polyposis in these patients.

Toxicity, pharmacokinetics, and in vitro hemodialysis clearance of ifosfamide and metabolites in an anephric pediatric patient with Wilms' tumor.

PURPOSE: We evaluated the in vitro hemodialysis ratio and subsequent toxicity and pharmacokinetics of ifosfamide in an anephric patient with Wilms' tumor. METHODS: An in vitro model was used to determine the extraction ratio of ifosfamide by dialysis. The toxicity and plasma concentrations of ifosfamide, chloroacetaldehyde, and 4-hydroxyifosfamide were then determined over 24 h after a single 1.6 g/m2 dose of ifosfamide. Plasma concentrations were also measured before and after ten dialysis sessions during four courses of ifosfamide therapy. RESULTS: The in vitro hemodialysis model showed that ifosfamide was cleared with an extraction ratio of 86.7+/-0.5% and remained constant even at low concentrations of drug. The mean decrease in vivo following hemodialysis for ifosfamide, chloroacetaldehyde, and 4-hydroxyifosfamide were 86.9%, 77.2%, and 36.2%, respectively. The pharmacokinetic parameters for ifosfamide using model-independent methods were calculated: Vd = 0.23 l/kg, t1/2 = 4.8 h, and ClT = 3.30 l/h per m2. Ifosfamide-associated neurotoxicity was noted within hours of drug administration and improved rapidly following hemodialysis. CONCLUSIONS: The results of our study suggest that the pharmacokinetics of parent ifosfamide may not be substantially altered in patients with renal failure. Hemodialysis was shown to remove ifosfamide, chloroacetaldehyde, and 4-hydroxyifosfamide from the blood stream. Hemodialysis was also shown to reverse ifosfamide-related neurotoxicity.

"Above all do no harm:" horizons in pediatric oncology.

The articles selected in this review highlight some advances in the use of the "old standards" methotrexate and 6-mercaptopurine for the treatment of children with acute lymphoblastic leukemia, especially the laboratory studies, which may allow a "pharmacologic phenotyping" to identify children most likely to relapse. In addition, we review the use of "newer" drugs (epipodophyllotoxins), which may be effective but are also associated with high morbidity (ie, secondary acute myeloid leukemia). As a second issue, "dose intensity" and the use of high-dose chemotherapy followed by bone marrow transplantation will be challenged, especially in light of peripheral stem cell harvest and the use of growth factors.

The folate receptor in central nervous system malignancies of childhood.

The folate receptor is a membrane linked glycoprotein that participates in the cellular accumulation of 5-methyltetrahydrofolic acid, methotrexate and 5,10-dideazatetrahydrofolic acid. Relative receptor overexpression has been observed in several malignant cell lines and tissues. In this study we determined receptor expression using western blot analysis in primary pediatric malignancies involving the central nervous system. This study suggests that ependymoma tumors have a high frequency of receptor expression which may reflect a specific cytogenetic abnormality or the cellular origin of these tumors. The potential role in developing selective chemotherapy mediated by the folate receptor is also discussed.

Pharmacokinetic evaluation of a new oral cyclosporine formulation.

STUDY OBJECTIVE: To compare the pharmacokinetics of a new oral cyclosporine preparation with those of cyclosporine solution diluted in Isocal and the intravenous formulation. DESIGN: Randomized, crossover trial. SETTING: Tertiary care referral center. PATIENTS: Seven pediatric liver transplant recipients who were receiving oral cyclosporine as part of their immunosuppressive regimen. All patients completed the study. INTERVENTIONS: Pharmacokinetic studies were performed with the intravenous and oral dosage forms. Patients received one dose of intravenous cyclosporine, and then were randomized to receive their usual oral cyclosporine dose incorporated into a chocolate wafer or mixed with Isocal. After a minimum of 3 days, the alternative preparation was administered. Serial cyclosporine blood samples were collected at predetermined intervals for 12 hours after the third dose for each regimen. Concentrations were determined by high-performance liquid chromatography. The data for the three dosage forms were fit simultaneously with a two-compartment model. MEASUREMENTS AND MAIN RESULTS: No difference was seen in F, ka, Cmax, and tmax between the two oral cyclosporine preparations (p > 0.05). No new rejection episodes occurred during the study period. CONCLUSIONS: We conclude there is no difference in the bioavailability of the oral solution and the chocolate formulation. We believe the new preparation may increase patient compliance and ensure administration of a complete dose compared with the currently marketed solution.

Phase I trial of paclitaxel in children with refractory solid tumors: a Pediatric Oncology Group Study.

PURPOSE: A phase I study was performed to describe the principal toxicities and identify the maximum-tolerated dose (MTD) of Taxol (paclitaxel; Bristol-Myers Squibb Co, Wallingford, CT) in children with therapy-resistant solid tumors. Additionally, the pharmacokinetic disposition of Taxol in children was studied, and preliminary evidence of the activity of Taxol against pediatric solid tumors was assessed. PATIENTS AND METHODS: Twenty-four-hour continuous infusions of Taxol were administered every 21 days to children (median age, 12 years; range, 2 to 22) with refractory solid tumors. Doses ranged from 200 to 420 mg/m2, there was no intrapatient dose escalation. RESULTS: A total of 62 courses of Taxol were administered to 31 patients. Two patients developed acute anaphylaxis during their second infusion of taxol at doses of 200 mg/m2 and 350 mg/m2, respectively. No other allergic reactions were documented. Myelosuppression occurred at all dose levels, but was of short duration (< or = 7 days) and did not appear to increase with consecutive courses or at higher dosage levels. A stocking-and-glove peripheral neuropathy became evident at doses > or = 290 mg/m2. Dose-limiting neurotoxicity occurred at 420 mg/m2 and comprised a significant fine-motor and peripheral neuropathy in one patient, and a tonic-clonic seizure in another. End-of-infusion plasma concentrations ranged from 0.40 to 6.4 mumol/L, and were not found to be dose-dependent over the range of doses studied. A complete response was documented in one patient, partial response in two, and minimal response in one for an overall response rate of 13%. CONCLUSION: Neurotoxicity was dose-limiting when Taxol was administered by 24-hour continuous infusion to pediatric patients with relapsed solid tumors. In this population, the recommended dose for phase II trials is 350 mg/m2/d.

Accumulation of 5-methyltetrahydrofolic acid and folylpolyglutamate synthetase expression by mitogen stimulated human lymphocytes.

The accumulation of 5-methyl[3H]tetrahydrofolic acid (5CH3[3H]FH4) by phytohaemagglutinin stimulated lymphocytes (PHA-L) cultured in folate free media was investigated to determine the mechanism of uptake of 5CH3FH4 and the requirement of the cells for this vitamin as assessed by monitoring de novo thymidine synthesis. When grown in 20 nM 5CH3[3H]FH4 PHA-L accumulate radiolabel at a rate of 0.04 pmol/h/10(6) cells. This doubles the endogenous folate pool of unstimulated cells (0.6 +/- 0.16 pmol/10(6) cells) in about 15 h. Uptake proceeded via a saturable process, independent of a high affinity folate receptor as assessed by ligand binding and by Northern and Western blot analysis. However, transport was blocked by probenecid, which is consistent with an anion carrier mechanism. Unstimulated cells lacked folypolyglutamate synthetase (FPGS) activity and did not express significant amounts of FPGS mRNA. After 48 h of mitogen stimulation there was a 4-10-fold increase in FPGS mRNA and folypolyglutamate formation (Glu > or = 5) was essentially simultaneous with 5CH3[3H]FH4 transport. Increasing extracellular folate to 2 microM only increased intracellular folate 8-fold, but the length of the folylpolyglutamates decreased. The increased folate did not increase de novo thymidine synthesis compared to cells grown in physiological folate. We conclude that mitogen stimulation activates the process(es) for folate accumulation, especially FPGS, and that physiological uptake (0.04 pmol/h/10(6) cells) is adequate for meeting the cells' need for the vitamin.

Subacute measles encephalitis in the young immunocompromised host: report of two cases diagnosed by polymerase chain reaction and treated with ribavirin and review of the literature.

Two young patients with subacute measles encephalitis are described: a 20-year-old male hemophiliac infected with human immunodeficiency virus (HIV) and a 4-year-old girl with acute leukemia. Both patients were afebrile and had persistent focal seizures and slurred speech beginning 2 and 7 months, respectively, after the onset of uncomplicated acute measles. The diagnosis of subacute measles encephalitis was established by demonstration of paramyxovirus nucleocapsid on electron microscopy of brain tissue in one case and by detection of measles virus genome with the polymerase chain reaction in both. Treatment of the HIV-infected man with intravenous ribavirin was begun when the patient lost consciousness after several weeks of seizures; he died. The girl with leukemia was treated early after the onset of symptoms and recovered after a 15-week course. Review of 31 previously published cases revealed a typical clinical presentation. Cerebrospinal fluid (CSF) analysis, electroencephalography, measurement of measles antibody in serum and CSF, and computed tomography of the brain were not helpful in the diagnosis of subacute measles encephalitis. In contrast, histologic examination of brain tissue proved useful in establishing the diagnosis. On the basis of our experience and our literature review, we conclude that histologic and polymerase chain reaction studies of brain tissue are required for the early diagnosis of subacute measles encephalitis and that therapy with intravenous ribavirin is effective when administered early.

Cellular localization of the folate receptor: potential role in drug toxicity and folate homeostasis.

In the past year, gp38, a glycosyl-phosphatidylinositol linked membrane protein that is overexpressed in some malignant tissues, has been shown to be the folate receptor. Using immunohistochemical techniques with the monoclonal antibody MOv19 against gp38, we evaluated the cellular localization of folate receptors in normal human tissues, which are potential target sites for drugs that utilize this uptake mechanism. The choroid plexus was intensely positive with staining limited to the epithelium, which in some foci had a distinct bilaminar pattern limited to the luminal and basal surfaces. The epithelium of the fallopian tube, uterus, and epididymis was highly immunoreactive. The acinar cells of the breast, submandibular salivary, and bronchial glands also showed intense staining as did the trophoblastic cells of the placenta. In the kidney reactivity was localized to the proximal tubules. Lung alveolar lining including type I and II pneumocytes stained intensely. Limited but focal reactivity was noted in the vas deferens, ovary, thyroid, and pancreas. This study in conjunction with previous work showing marked overexpression of folate receptor in some malignant cells suggests that the folate receptor may be an important target for diagnostic or therapeutic exploitation and indicates sites of potential drug toxicity.