Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 13 de 13
Filtrar
1.
Sci Rep ; 4: 6163, 2014 Aug 22.
Artículo en Inglés | MEDLINE | ID: mdl-25145385

RESUMEN

An important step forward for the understanding of high-temperature superconductivity has been the discovery of iron-based superconductors. Among these compounds, iron pnictides could be used for high-field magnet applications, resulting more advantageous over conventional superconductors, due to a high upper critical field as well as its low anisotropy at low temperatures. However, the principal obstacle in fabricating high quality superconducting wires and tapes is given by grain boundaries. In order to study these effects, the dc transport and voltage-noise properties of Co-doped BaFe2As2 superconducting films with artificial grain boundary junctions have been investigated. A specific procedure allows the separation of the film noise from that of the junction. While the former shows a standard 1/f behaviour, the latter is characterized by an unconventional temperature-dependent multi-Lorentzian voltage-spectral density. Moreover, below the film superconducting critical temperature, a peculiar noise spectrum is found for the grain boundary junction. Possible theoretical interpretation of these phenomena is proposed.

2.
Ann Oncol ; 20(6): 1062-7, 2009 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-19218305

RESUMEN

BACKGROUND: This clinical trial assessed the efficacy of pemetrexed combined with oxaliplatin (PEMOX) in patients with advanced gastric cancer (AGC). PATIENTS AND METHODS: Forty-four patients with untreated AGC were enrolled to evaluate response rate (RR). Patients received pemetrexed (500 mg/m(2)) with vitamin supplementation and oxaliplatin (120 mg/m(2)) every 21 days for six cycles or until disease progression occurred. RESULTS: Median age was 62 years (range 26-76). The majority of patients (93%) had metastatic disease. Sixteen of the 44 patients achieved confirmed response [RR 36%; 95% confidence interval (CI) 22% to 52%]; four complete responses and 12 partial responses (complete and partial responses according to the RECIST guidelines are the confirmed-responses observed in the study population). Median time to tumor progression (TTP) was 6.2 months (95% CI 4.3-7.5) and median survival was 10.8 months (95% CI 7.7-17.2). A total of 220 cycles were administered, with a median of six cycles. Most common grade 3/4 toxic effects were neutropenia in 41% of patients (19% of cycles) and thrombocytopenia in 11% of patients (4% of cycles). Treatment delays or dose reductions for toxicity occurred in 10% and 5% of cycles, respectively. CONCLUSIONS: PEMOX is active and well tolerated in AGC. RR, TTP, and survival were comparable to those achieved in studies using different 5-fluorouracil (5-FU)-oxaliplatin combinations, without the inconvenience of prolonged 5-FU schedules.


Asunto(s)
Adenocarcinoma/tratamiento farmacológico , Protocolos de Quimioterapia Combinada Antineoplásica/uso terapéutico , Neoplasias Gástricas/tratamiento farmacológico , Adenocarcinoma/patología , Adenocarcinoma/secundario , Adulto , Anciano , Femenino , Glutamatos/administración & dosificación , Guanina/administración & dosificación , Guanina/análogos & derivados , Humanos , Masculino , Persona de Mediana Edad , Compuestos Organoplatinos/administración & dosificación , Oxaliplatino , Pemetrexed , Neoplasias Gástricas/patología , Neoplasias Gástricas/secundario
3.
Br J Cancer ; 96(1): 21-8, 2007 Jan 15.
Artículo en Inglés | MEDLINE | ID: mdl-17164761

RESUMEN

Several schedules of 5-fluorouracil (FU) and irinotecan (IRI) have been shown to improve overall survival in advanced colorectal cancer (CRC). Preclinical evidence suggests that the sequential administration of IRI and FU produces synergistic activity, although their clinical use has not been fully optimised. We investigated the interaction between short-term exposure to SN-38, the active metabolite of IRI, and prolonged exposure to FU in human CRC HT-29 cells and observed that the synergism of action between the two agents can be increased by extending the time of cell exposure to FU and reducing the interval between administration of the two agents. Based on these findings, we performed a phase I trial in 25 advanced CRC patients using a modified IRI/FU regimen as first-line therapy and evaluated three dose levels of IRI (150-300 mg/m(2)) and two of continuous infusion of FU (800-1000 mg/m(2)) in a 3-weekly schedule. The most severe grade III-IV toxicities were neutropoenia in four cycles and diarrhoea in three. One patient achieved complete response (4%), 12 a partial response (48%), the overall response rate was 52% (+/-20, 95% CI); seven of 25 patients had stable disease (28%), the overall disease control was 80% (+/-16, 95% CI). This modified IRI/FU schedule is feasible and exhibits potentially interesting clinical activity.


Asunto(s)
Protocolos de Quimioterapia Combinada Antineoplásica/uso terapéutico , Camptotecina/análogos & derivados , Neoplasias Colorrectales/tratamiento farmacológico , Fluorouracilo/administración & dosificación , Adulto , Anciano , Protocolos de Quimioterapia Combinada Antineoplásica/efectos adversos , Apoptosis/efectos de los fármacos , Camptotecina/administración & dosificación , Camptotecina/efectos adversos , Camptotecina/farmacología , Ciclo Celular/efectos de los fármacos , Proliferación Celular/efectos de los fármacos , Quimioterapia Adyuvante , Estudios de Cohortes , Progresión de la Enfermedad , Relación Dosis-Respuesta a Droga , Esquema de Medicación , Sinergismo Farmacológico , Estudios de Factibilidad , Femenino , Fluorouracilo/efectos adversos , Fluorouracilo/farmacología , Células HT29 , Humanos , Infusiones Intravenosas , Irinotecán , Masculino , Dosis Máxima Tolerada , Persona de Mediana Edad , Recurrencia , Resultado del Tratamiento
4.
Oncology ; 70(5): 366-77, 2006.
Artículo en Inglés | MEDLINE | ID: mdl-17179731

RESUMEN

OBJECTIVE: The combined assessment of thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD) and thymidine phosphorylase (TP) gene expressions in metastatic colorectal cancer has been reported to be able to predict the efficacy of fluoropyrimidine-based chemotherapy. In order to evaluate the prognostic role in the adjuvant setting, we investigated the TS, DPD and TP expression in primary tumors of colorectal cancer patients treated with 5-fluorouracil (5-FU). METHODS: TS, DPD and TP expression levels were determined by immunohistochemistry in paraffin-embedded primary tumor tissues from 62 patients with Dukes' stage B and C colorectal cancers who underwent surgery and received adjuvant systemic chemotherapy with 5-FU. The median follow-up was 90 months (range 17-127). RESULTS: Dukes' stage C cancer and high TS expression were independent markers of poor prognosis for disease-free survival (DFS; p = 0.0009 and p = 0.007, respectively) and overall survival (OS; p = 0.0005 and p = 0.011, respectively). By multivariate analysis, patients with high DPD expression had significantly shorter DFS (p = 0.007) and OS (p = 0.005) compared to patients with low DPD expression. In the combined analysis of 2 markers, patients with low TS and low DPD had the best outcome in terms of DFS (p = 0.007) and OS (p = 0.03). The analysis of all 3 proteins showed that the patients with low expression of all 3 markers had significantly longer DFS (p = 0.04) and OS (p = 0.01) than patients with a high value of any one of the protein expressions. However, the joint analysis of 3 markers (group with TS-/DPD-/TP-) could not identify a subgroup of patients with a better prognosis compared to the analysis of 2 markers (group with TS-/DPD-). The analysis of Dukes' stage C cancer patients confirmed a significant benefit in terms of DFS and OS (p = 0.001 and p = 0.006, respectively) when all 3 markers had low expression. We also found a positive significant correlation between TS and TP protein expression (p = 0.033). CONCLUSIONS: This retrospective investigation suggests that the combined assessment of TS and DPD may be useful to evaluate the prognosis of patients with Dukes' B and C colon carcinoma receiving 5-FU adjuvant chemotherapy. The role of TP as a predictor for 5-FU-based therapy needs further investigations.


Asunto(s)
Antimetabolitos Antineoplásicos/uso terapéutico , Biomarcadores de Tumor/metabolismo , Neoplasias Colorrectales/tratamiento farmacológico , Neoplasias Colorrectales/enzimología , Dihidrouracilo Deshidrogenasa (NADP)/metabolismo , Fluorouracilo/uso terapéutico , Timidina Fosforilasa/metabolismo , Timidilato Sintasa/metabolismo , Anciano , Quimioterapia Adyuvante , Neoplasias Colorrectales/patología , Neoplasias Colorrectales/cirugía , Supervivencia sin Enfermedad , Femenino , Regulación Enzimológica de la Expresión Génica , Regulación Neoplásica de la Expresión Génica , Humanos , Inmunohistoquímica , Masculino , Persona de Mediana Edad , Análisis Multivariante , Estadificación de Neoplasias , Valor Predictivo de las Pruebas , Pronóstico , Estudios Retrospectivos , Factores de Tiempo
5.
Eur J Cancer ; 38(4): 527-34, 2002 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-11872345

RESUMEN

Recent investigations have focused on the prognostic value of thymidylate synthase (TS) assessment in metastases of colorectal carcinoma (CRC). In order to evaluate the prognostic impact of TS expression after resection of metastases of colorectal cancer followed by systemic adjuvant chemotherapy, we performed an immunohistochemical characterisation of TS in the primary tumours and in the corresponding radically resected hepatic and pulmonary metastases. An additional objective was to compare the levels of TS in primary and metastatic disease. TS expression was assessed by immunohistochemistry using the monoclonal antibody TS 106. The study population consisted of 60 patients: 48 underwent liver and 12 lung resection. All of them received adjuvant chemotherapy after metastasectomy according to the Mayo Clinic schedule. In the 49 evaluable primary tumours, TS score was high in 53% and low in 47% of patients, while in the 60 metastatic samples TS immunostaining was high in 33% and low in 67%. There was a significantly smaller number of high TS expressors in metastatic than in primary tumours (P<0.04). No correlation was observed between TS expression and the site of the metastasis. TS status did not significantly correlate with the median disease-free interval (DFI) after metastasectomy, although this parameter was longer for patients with low TS immunoreactivity in the resected metastases than for those with high TS lesions (19.6 versus 13.8 months). Patients with high TS levels, however, had a significantly shorter median overall survival (OS) (27.6 months) than those with low TS expression (36.3 months) (P<0.008). TS status in the resected metastases confirmed its independent prognostic value in the multivariate analysis and was the only prognostic marker of OS in the subgroup of patients with resected liver metastases. These results suggest that high TS levels in resected metastases of colorectal cancer are associated with a poor outcome after surgery and 5-FU adjuvant therapy; therefore, a prospective assessment of TS levels in resected colorectal metastases could be useful to define which patients will most likely benefit from 5-FU adjuvant therapy after metastasectomy. Chemotherapeutic agents that target TS may not be the appropriate adjuvant treatment after metastasectomy for patients with a high TS expression in the resected metastases of colorectal cancer.


Asunto(s)
Biomarcadores de Tumor/metabolismo , Neoplasias Colorrectales/enzimología , Neoplasias Hepáticas/enzimología , Neoplasias Pulmonares/enzimología , Timidilato Sintasa/metabolismo , Adulto , Anciano , Protocolos de Quimioterapia Combinada Antineoplásica/uso terapéutico , Quimioterapia Adyuvante , Neoplasias Colorrectales/tratamiento farmacológico , Supervivencia sin Enfermedad , Femenino , Fluorouracilo/administración & dosificación , Estudios de Seguimiento , Humanos , Inmunohistoquímica , Leucovorina/administración & dosificación , Neoplasias Hepáticas/tratamiento farmacológico , Neoplasias Hepáticas/secundario , Neoplasias Pulmonares/tratamiento farmacológico , Neoplasias Pulmonares/secundario , Masculino , Persona de Mediana Edad , Pronóstico
6.
Ann Oncol ; 9(11): 1199-204, 1998 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-9862050

RESUMEN

PURPOSE: This multicenter phase II study was designed to assess the efficacy of the alternating schedule of irinotecan (CPT-11) with bolus 5-fluorouracil (5-FU) and leucovorin (LV) in first-line chemotherapy for metastatic colorectal cancer (CRC). PATIENTS AND METHODS: Patients with histologically proven metastatic colorectal cancer, and at least one bidimensionally measurable lesion, aged 18-70, with performance status < or = 2, normal baseline biological values and no prior chemotherapy (or only adjuvant chemotherapy completed > or = 6 months before study entry) were selected. Treatment was irinotecan 350 mg/m2, i.v., day 1, alternating with leucovorin 20 mg/m2 i.v. and 5-FU 425 mg/m2, i.v. daily for five consecutive days, day 22-26 (Mayo Clinic regimen). One alternating cycle was to be performed every six weeks. Patients were evaluated for efficacy every alternating cycle. Treatment was administered until five alternating cycles, disease progression, unacceptable toxicity or patient refusal. RESULTS: Thirty-three patients (28 chemotherapy-naïve and five with prior adjuvant treatment completed > 1 year prior to accrual) were enrolled. The objective response rate (RR) was 30% (95% CI: 16-49; 10 patients/33; nine partial response and one complete response). All responses were reviewed by an independent external review committee. An additional 49% of patients had stable disease. The median survival was 16 months, the one year survival amounted to 58% and the median progression free survival was 7.2 months. Relative dose intensity was nearly 90% for both drugs. Grade 3-4 diarrhea and neutropenia were the most frequent severe toxic events, seen in 24% and 64% of patients, respectively. CONCLUSIONS: The alternating schedule of CPT-11 350 mg/m2 with five days bolus of 5-FU and low dose LV is an active and feasible regimen as front-line therapy for metastatic CRC. It is well tolerated, without evidence of overlapping toxicity. The response rate appears promising with regard to that expected with either single agent. This regimen warrants further assessment in randomized trials.


Asunto(s)
Protocolos de Quimioterapia Combinada Antineoplásica/uso terapéutico , Neoplasias Colorrectales/tratamiento farmacológico , Adulto , Anciano , Protocolos de Quimioterapia Combinada Antineoplásica/administración & dosificación , Camptotecina/administración & dosificación , Camptotecina/análogos & derivados , Neoplasias Colorrectales/patología , Esquema de Medicación , Femenino , Fluorouracilo/administración & dosificación , Humanos , Irinotecán , Leucovorina/administración & dosificación , Masculino , Persona de Mediana Edad , Metástasis de la Neoplasia , Análisis de Supervivencia
7.
J Virol ; 72(11): 9233-46, 1998 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-9765471

RESUMEN

Virus-like particles (VLPs) are being evaluated as a candidate rotavirus vaccine. The immunogenicity and protective efficacy of different formulations of VLPs administered parenterally to rabbits were tested. Two doses of VLPs (2/6-, G3 2/6/7-, or P[2], G3 2/4/6/7-VLPs) or SA11 simian rotavirus in Freund's adjuvants, QS-21 (saponin adjuvant), or aluminum phosphate (AlP) were administered. Serological and mucosal immune responses were evaluated in all vaccinated and control rabbits before and after oral challenge with 10(3) 50% infective doses of live P[14], G3 ALA lapine rotavirus. All VLP- and SA11-vaccinated rabbits developed high levels of rotavirus-specific serum and intestinal immunoglobulin G (IgG) antibodies but not intestinal IgA antibodies. SA11 and 2/4/6/7-VLPs afforded similar but much higher mean levels of protection than 2/6/7- or 2/6-VLPs in QS-21. The presence of neutralizing antibodies to VP4 correlated (P < 0.001, r = 0.55; Pearson's correlation coefficient) with enhanced protection rates, suggesting that these antibodies are important for protection. Although the inclusion of VP4 resulted in higher mean protection levels, high levels of protection (87 to 100%) from infection were observed in individual rabbits immunized with 2/6/7- or 2/6-VLPs in Freund's adjuvants. Therefore, neither VP7 nor VP4 was absolutely required to achieve protection from infection in the rabbit model when Freund's adjuvant was used. Our results show that VLPs are immunogenic when administered parenterally to rabbits and that Freund's adjuvant is a better adjuvant than QS-21. The use of the rabbit model may help further our understanding of the critical rotavirus proteins needed to induce active protection. VLPs are a promising candidate for a parenterally administered subunit rotavirus vaccine.


Asunto(s)
Infecciones por Rotavirus/inmunología , Infecciones por Rotavirus/prevención & control , Rotavirus/inmunología , Vacunas Sintéticas/administración & dosificación , Vacunas Virales/administración & dosificación , Adyuvantes Inmunológicos/administración & dosificación , Compuestos de Aluminio/administración & dosificación , Animales , Anticuerpos Antivirales/biosíntesis , Anticuerpos Antivirales/sangre , Modelos Animales de Enfermedad , Heces/virología , Femenino , Adyuvante de Freund/administración & dosificación , Haplorrinos , Inmunoglobulina A/biosíntesis , Inmunoglobulina G/biosíntesis , Inyecciones Intramusculares , Intestinos/inmunología , Masculino , Fosfatos/administración & dosificación , Conejos , Rotavirus/aislamiento & purificación , Infecciones por Rotavirus/virología , Saponinas/administración & dosificación , Vacunación , Proteínas Estructurales Virales/inmunología
8.
G Chir ; 18(10): 646-52, 1997 Oct.
Artículo en Italiano | MEDLINE | ID: mdl-9479979

RESUMEN

The Authors experience in five retroperitoneal tumors with symptoms and histopathological characteristics not different from those described in the Literature, is here reported. Topographic findings, classification, and incidence of retroperitoneal tumors as referred by various Authors are discussed. Two aspects are particularly pointed out: the histological type and the surgical strategy for their removal. Concerning the first aspect, the Authors underline that benign lesion may have an optimal outcome and a long survival, unlike the malignant ones, which have always unfavourable prognosis, despite adjuvant and complementary therapy (radiotherapy, chemotherapy). As for the second aspect, surgery is the treatment of choice even when other organs different from those exclusively retroperitoneal, may be involved in the demolition.


Asunto(s)
Neoplasias Retroperitoneales , Adulto , Anciano , Anciano de 80 o más Años , Angiofibroma/diagnóstico por imagen , Angiofibroma/patología , Angiofibroma/cirugía , Angiomiolipoma/diagnóstico por imagen , Angiomiolipoma/patología , Angiomiolipoma/cirugía , Resultado Fatal , Femenino , Humanos , Leiomioma/diagnóstico por imagen , Leiomioma/patología , Leiomioma/cirugía , Leiomiosarcoma/diagnóstico por imagen , Leiomiosarcoma/patología , Leiomiosarcoma/cirugía , Masculino , Persona de Mediana Edad , Neoplasias Retroperitoneales/diagnóstico por imagen , Neoplasias Retroperitoneales/patología , Neoplasias Retroperitoneales/cirugía , Sarcoma/diagnóstico por imagen , Sarcoma/patología , Sarcoma/cirugía , Ultrasonografía
9.
Neurosurgery ; 37(6): 1075-9, 1995 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-8584147

RESUMEN

Transfusion of homologous blood is associated with significant and well-known risks. Reported transfusion rates for pediatric patients undergoing surgical correction of synostotic calvarial sutures vary between 20 and 500% of estimated blood volume. The objective of this study was to ascertain the risks, benefits, and effects on transfusion rates associated with the use of intraoperative autologous transfusion (IAT) in this patient population. The Haemonetics Cell Saver 4 (Haemonetics Corporation, Braintree, MA) autotransfusion system was used to salvage blood in 18 patients undergoing the release of stenosed calvarial sutures. In a prospective, nonrandomized study, these patients were compared with a control group of similar age, gender, weight, and surgical procedures. There were 10 male patients and 8 female patients; the mean age was 7.2 months, the mean weight was 8.67 kg, and the mean surgical time was 3.15 hours. The mean amount of homologous blood transfused to the control group was 189 ml, compared with 87.69 ml for the IAT group, which was a decrease of 46.3%. The mean amount of autologous blood transfused was 150 ml (range, 50-250 ml). Thirty-three percent of the patients in the IAT group did not require homologous blood transfusion. No complications were observed with the use of the Cell Saver in the IAT group. The use of the Cell Saver was associated with a significant decrease in the amount and rate of homologous blood transfusions. Its use appears to be safe in pediatric patients undergoing craniosynostotic surgery.


Asunto(s)
Pérdida de Sangre Quirúrgica/fisiopatología , Transfusión de Sangre Autóloga/instrumentación , Craneosinostosis/cirugía , Volumen Sanguíneo/fisiología , Separación Celular/instrumentación , Craneosinostosis/fisiopatología , Craneotomía/instrumentación , Femenino , Humanos , Lactante , Masculino
10.
Med Oncol Tumor Pharmacother ; 8(2): 69-73, 1991.
Artículo en Inglés | MEDLINE | ID: mdl-1749302

RESUMEN

Ninety-six patients with colorectal cancer (stage B2-C) were randomized to the control arm or to receive adjuvant chemotherapy with folinic acid, FU and MMC. Ninety-three patients are evaluable. The median follow up is 12 months. The average time between surgery and the start of therapy is 28 days. Toxicity is evaluable in 36 of 41 treated patients. Four patients (10%) failed to complete the projected treatment due to toxicity. Toxicity observed in 208 courses of therapy was mostly gastrointestinal and hematological. No cases of treatment related death or cancer-associated hemolytic uremic syndrome (C-HUS) were reported. The average relative dose intensity (rDI) of the projected treatment was 82.6%. Our study is ongoing and further patients are required to achieve statistically significant results.


Asunto(s)
Protocolos de Quimioterapia Combinada Antineoplásica/efectos adversos , Neoplasias Colorrectales/tratamiento farmacológico , Quimioterapia Adyuvante , Neoplasias Colorrectales/cirugía , Evaluación de Medicamentos , Femenino , Fluorouracilo/administración & dosificación , Humanos , Leucovorina/administración & dosificación , Masculino , Persona de Mediana Edad , Mitomicina/administración & dosificación
11.
Eur J Cancer Clin Oncol ; 23(9): 1303-6, 1987 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-3500048

RESUMEN

The therapeutic activity of 5-FU in large bowel cancer is enhanced by increasing the intracellular pool of reduced folates. We treated 45 patients with advanced colon cancer with HDFA and 5-FU for 5 consecutive days. None had been given previous radio- or chemotherapy. All had measurable disease. Not one complete response was observed. Thirteen of the 39 evaluable patients showed partial response. Median duration of response was 9+ months. The probability of 50% survival was 15 months for all evaluable patients. There was no case of severe toxicity and the principal toxic effects were oral mucositis and diarrhea. To date, HDFA + 5-FU is one of the most effective treatments for large bowel cancer.


Asunto(s)
Protocolos de Quimioterapia Combinada Antineoplásica/uso terapéutico , Neoplasias del Colon/tratamiento farmacológico , Neoplasias del Recto/tratamiento farmacológico , Adulto , Anciano , Neoplasias del Colon/mortalidad , Diarrea/inducido químicamente , Femenino , Fluorouracilo/administración & dosificación , Fluorouracilo/efectos adversos , Humanos , Leucovorina/administración & dosificación , Leucovorina/efectos adversos , Neoplasias Hepáticas/secundario , Masculino , Persona de Mediana Edad , Mucosa Bucal , Neoplasias del Recto/mortalidad , Estomatitis/inducido químicamente
12.
Ric Clin Lab ; 14(2): 211-20, 1984.
Artículo en Inglés | MEDLINE | ID: mdl-6091246

RESUMEN

The effect of administration of a synthetic ACTH analogue (ACTH 1-17, Synchrodyn) in the chemotherapy of advanced-phase solid tumors was studied. In this preliminary report the following data are evaluated: response rate; occurrence of toxic effects; performance status of patients; several immunological parameters. The administration of Synchrodyn seems mainly to influence the lymphocyte subpopulations and the occurrence of toxic effects. A final evaluation of the role that may be played by chronotherapy in the treatment of tumors must await further studies on the clinical response and tolerance.


Asunto(s)
Hormona Adrenocorticotrópica/uso terapéutico , Neoplasias/tratamiento farmacológico , Fragmentos de Péptidos/uso terapéutico , Hormona Adrenocorticotrópica/farmacología , Ritmo Circadiano/efectos de los fármacos , Esquema de Medicación , Quimioterapia Combinada , Humanos , Inmunidad/efectos de los fármacos , Linfocitos/efectos de los fármacos , Fragmentos de Péptidos/farmacología
SELECCIÓN DE REFERENCIAS
DETALLE DE LA BÚSQUEDA