RESUMEN
PURPOSE: Breast cancer (BC) is the most frequent neoplasm in women in Colombia and is associated with a higher mortality rate than in other countries and regions. Neoadjuvant chemotherapy (NACT) has become a standard treatment in locally advanced BC and provides an opportunity to improve clinical outcomes in BC. This study aims to describe characteristics, treatment patterns, and outcomes after NACT in a cohort of Colombian patients with BC. METHODS: We performed a retrospective cohort study. We included adult patients with BC treated with NACT. Clinical charts were retrospectively reviewed. Descriptive statistics and time to event for overall survival analyses were performed. Recursive partitioning was performed for survival curves to assess the complex relationship between survival times and other variables. RESULTS: Three hundred and fourteen patients were included for analysis. The pathologic complete response after neoadjuvant chemotherapy (ypCR) rate was 34.4%, with a higher ypCR in triple-negative BC (TNBC; 46.9%) and human epidermal growth factor receptor 2-positive BC (72.7%). Those who did not achieve ypCR had a higher percentage of death and relapse. The median follow-up was 4.9 years, with an 88.2% 5-year overall survival (OS). CONCLUSION: A total of 62.6% of the total patients identified were not treated with NACT, indicating a low utilization. Our global ypCR rate was higher when compared with similar studies in Colombia, likely because of differences in the NACT treatment regimens. ypCR was only associated with OS in the TNBC subgroup, emphasizing the importance of pursuing ypCR in these patients. We consider the use of NACT a valuable opportunity to implement innovative treatment approaches that improve outcomes in Colombian patients with BC.
Asunto(s)
Neoplasias de la Mama , Terapia Neoadyuvante , Humanos , Femenino , Terapia Neoadyuvante/métodos , Estudios Retrospectivos , Persona de Mediana Edad , Neoplasias de la Mama/tratamiento farmacológico , Neoplasias de la Mama/patología , Neoplasias de la Mama/mortalidad , Colombia , Adulto , Anciano , Quimioterapia Adyuvante , Resultado del TratamientoRESUMEN
BACKGROUND: In Colombia and worldwide, breast cancer (BC) is the most frequently diagnosed neoplasia and the leading cause of death from cancer among women. Studies predominantly involve hereditary and familial cases, demonstrating a gap in the literature regarding the identification of germline mutations in unselected patients from Latin-America. Identification of pathogenic/likely pathogenic (P/LP) variants is important for shaping national genetic analysis policies, genetic counseling, and early detection strategies. The present study included 400 women with unselected breast cancer (BC), in whom we analyzed ten genes, using Whole Exome Sequencing (WES), know to confer risk for BC, with the aim of determining the genomic profile of previously unreported P/LP variants in the affected population. Additionally, Multiplex Ligation-dependent Probe Amplification (MLPA) was performed to identify Large Genomic Rearrangements (LGRs) in the BRCA1/2 genes. To ascertain the functional impact of a recurrent intronic variant (ATM c.5496 + 2_5496 + 5delTAAG), a minigene assay was conducted. RESULTS: We ascertained the frequency of P/LP germline variants in BRCA2 (2.5%), ATM (1.25%), BRCA1 (0.75%), PALB2 (0.50%), CHEK2 (0.50%), BARD1 (0.25%), and RAD51D (0.25%) genes in the population of study. P/LP variants account for 6% of the total population analyzed. No LGRs were detected in our study. We identified 1.75% of recurrent variants in BRCA2 and ATM genes. One of them corresponds to the ATM c.5496 + 2_5496 + 5delTAAG. Functional validation of this variant demonstrated a splicing alteration probably modifying the Pincer domain and subsequent protein structure. CONCLUSION: This study described for the first time the genomic profile of ten risk genes in Colombian women with unselected BC. Our findings underscore the significance of population-based research, advocating the consideration of molecular testing in all women with cancer.
Asunto(s)
Proteína BRCA2 , Neoplasias de la Mama , Predisposición Genética a la Enfermedad , Mutación de Línea Germinal , Humanos , Femenino , Mutación de Línea Germinal/genética , Neoplasias de la Mama/genética , Neoplasias de la Mama/patología , Neoplasias de la Mama/epidemiología , Colombia/epidemiología , Persona de Mediana Edad , Adulto , Proteína BRCA2/genética , Proteína BRCA1/genética , Secuenciación del Exoma , Anciano , Pruebas Genéticas/métodos , Proteínas de la Ataxia Telangiectasia Mutada/genéticaRESUMEN
Introduction: During the pandemic, it has been recommended that vaccination against COVID-19 be a priority for patients with cancer; however, these patients were not included in the initial studies evaluating the available vaccines. Objective: To define the impact of vaccination against COVID-19 in preventing the risk of complications associated with the infection in a cohort of patients with cancer in Colombia. Methods: An analytical observational cohort study, based on national registry of patients with cancer and COVID 19 infection ACHOC-C19, was done. The data was collected from June 2021, until October 2021. Inclusion criteria were: Patients older than 18 years with cancer diagnosis and confirmed COVID-19 infection. Data from the unvaccinated and vaccinated cohorts were compared. Outcomes evaluated included all-cause mortality within 30 days of COVID-19 diagnosis, hospitalization, and need for mechanical ventilation. The estimation of the effect was made through the relative risk (RR), the absolute risk reduction (ARR) and the number needed to treat (NNT). Multivariate analysis was performed using generalized linear models. Results: 896 patients were included, of whom 470 were older than 60 years (52.4%) and 59% were women (n=530). 172 patients were recruited in the vaccinated cohort and 724 in the non-vaccinated cohort (ratio: 1 to 4.2). The cumulative incidence of clinical outcomes among the unvaccinated vs vaccinated patients were: for hospitalization 42% (95% CI: 38.7%-46.1%) vs 29%; (95% CI: 22.4%-36.5%); for invasive mechanical ventilation requirement 8.4% (n=61) vs 4.6% (n=8) and for mortality from all causes 17% (n=123) vs 4.65% (n=8). Conclusion: In our population, unvaccinated patients with cancer have an increased risk of complications for COVID -19 infection, as hospitalization, mechanical ventilation, and mortality. It is highly recommended to actively promote the vaccination among this population.
RESUMEN
To describe the population with early malignant melanoma, we performed a cohort study on the basis of the Epidemiological Registry of Malignant Melanoma in Colombia-Asociacion Colombiana de Hematologia y Oncologia. From January 2011 until December 2021, 759 patients were included; the average age was 66 years, 57% were women, acral lentiginous histology was found in 27.8% of patients, and the median follow-up was 36.5 months. The prognostic factors for overall survival in our population are Eastern Cooperative Oncology Group 3-4 (hazard ratio [HR], 13.8), stage III (HR, 5.07), received radiotherapy (HR, 3.38), ulceration on histology (HR, 2.68), chronic sun exposure (HR, 2.3), low income (HR, 2.04), previous local surgery (HR, 0.27), and have received adjuvant treatment (HR, 0.41).
Asunto(s)
Melanoma , Humanos , Femenino , Anciano , Masculino , Estudios de Cohortes , Pronóstico , Colombia/epidemiología , América Latina , Melanoma/diagnóstico , Melanoma/epidemiología , Melanoma/terapia , Sistema de Registros , Melanoma Cutáneo MalignoRESUMEN
PURPOSE: Identifying actionable oncogenic mutations have changed the therapeutic landscape in different types of tumors. This study investigated the utility of comprehensive genomic profiling (CGP), a hybrid capture-based next-generation sequencing (NGS) assay, in clinical practice in a developing country. METHODS: In this retrospective cohort study, CGP was performed on clinical samples from patients with different solid tumors recruited between December 2016 and November 2020, using hybrid capture-based genomic profiling, at the individual treating physicians' request in the clinical care for therapy decisions. Kaplan-Meier survival curves were estimated to characterize the time-to-event variables. RESULTS: Patients median age was 61 years (range: 14-87 years), and 64.7% were female. The most common histological diagnosis was lung primary tumors, with 90 patients corresponding to 52.9% of the samples (95% CI 45.4-60.4%). Actionable mutations with FDA-approved medications for specific alterations correspondent to tumoral histology were identified in 58 cases (46.4%), whereas other alterations were detected in 47 different samples (37.6%). The median overall survival was 15.5 months (95% CI 11.7 months-NR). Patients who were subjected to genomic evaluation at diagnosis reached a median overall survival of 18.3 months (95% CI 14.9 months-NR) compared to 14.1 months (95% CI 11.1 months-NR) in patients who obtained genomic evaluation after tumor progression and during standard treatment (P = .7). CONCLUSION: CGP of different types of tumors identifies clinically relevant genomic alterations that have benefited from targeted therapy and improve cancer care in a developing country to guide personalized treatment to beneficial outcomes of cancer patients.
Asunto(s)
Países en Desarrollo , Neoplasias Pulmonares , Humanos , Femenino , Persona de Mediana Edad , Masculino , Estudios Retrospectivos , Neoplasias Pulmonares/patología , Mutación , Genómica , Secuenciación de Nucleótidos de Alto RendimientoRESUMEN
Nivolumab is a human programmed death receptor-1 blocking antibody, used as treatment option in patients with advanced non-small-cell lung cancer (NSCLC). We assessed the nivolumab efficacy in terms of survival and response to treatment as second-line (2L) or third-line (3L) therapy in patients with advanced NSCLC. This is a multicentric observational study. Data of patients with advanced NSCLC who received nivolumab as 2L or 3L treatment were analyzed retrospectively. Information regarding patient demographics and clinical backgrounds, treatment patterns from diagnosis to post-nivolumab treatment, effectiveness, and safety of nivolumab treatment were collected. The outcomes evaluated were overall survival (OS), progression-free survival (PFS), and objective response rate (ORR) to treatment. OS and PFS were estimated with the Kaplan-Meier method and the differences were evaluated through the log-rank test. Data of 178 patients were included. The median follow-up was 26.8 months (interquartile range (IQR): 20.3-40.4). Nivolumab was commonly used as a 2L treatment (77.5%). The outcomes in this setting (2L) were as follows: ORR was 21.0%, and the median PFS and OS were 5.5 months (95% confidence interval (CI): 4.5-6.5) and 12.4 months (95% CI: 10.8-14.0), respectively. In 3L, the ORR with nivolumab was 15.0%, the median PFS and OS were 4.1 months (95% CI: 3.1-5.1) and 10.1 months (95% CI: 9.4-10.6), respectively. Three patients (1.7%) required discontinuation due to toxicity. Nivolumab effectiveness and safety in this scenario was consistent with that reported by previous trials and other real-world data.
Asunto(s)
Carcinoma de Pulmón de Células no Pequeñas , Neoplasias Pulmonares , Humanos , Carcinoma de Pulmón de Células no Pequeñas/tratamiento farmacológico , Nivolumab/uso terapéutico , Nivolumab/efectos adversos , Neoplasias Pulmonares/tratamiento farmacológico , Estudios Retrospectivos , Países en Desarrollo , Resultado del TratamientoRESUMEN
In a multiday conference, a panel of Latin American experts in biological cancer therapies and health economics were provided with questions to address the barriers restricting access to biosimilars in Latin America, specifically for patients with breast cancer and colorectal cancer, for whom biosimilars can be a path forward to increasing access to care. During the conference, responses were discussed and edited until a consensus was achieved. The regulatory challenges identified in the conference included heterogenous regulations, non-adherence to regulatory pathways, scarcity of market opportunity, inadequate naming of biosimilars by only using international non-proprietary names, imprecise use of interchangeability and substitution, and insufficient traceability and pharmacovigilance. Recommendations were developed to improve the implementation of regulatory pathways and reliable procurement strategies that increase access to these therapies with adequate traceability and outcome measures; efforts from all involved stakeholders will be crucial. These recommendations can serve as a strategy for biosimilar adoption in other countries in a similar situation.
Asunto(s)
Biosimilares Farmacéuticos , Neoplasias de la Mama , Neoplasias Colorrectales , Biosimilares Farmacéuticos/efectos adversos , Neoplasias de la Mama/tratamiento farmacológico , Neoplasias Colorrectales/tratamiento farmacológico , Femenino , Humanos , América Latina/epidemiología , FarmacovigilanciaRESUMEN
INTRODUCTION/BACKGROUND: Multiple Myeloma (MM) is a plasma cell derived clonal disorder that represents around 1% of all newly diagnosed neoplasms. Limited data regarding MM treatment in Latin America is available, and access to novel agents for a substantial portion of the population is limited by their high costs. MATERIALS (OR PATIENTS) AND METHODS: RENEHOC is a bidirectional (retrospective and prospective) multicenter observational registry of hematological malignancies in Colombia. MM patients included up to July 2020 were analyzed on this report. RESULTS: 890 are reported with a median follow-up of 18 months (IQR: 7-42 months). Patients were classified by age group (≤ or > 65 years). Median age at diagnosis was 67 years (IQR: 59-75 years) and 47.1% of patients were women. 709 patients (79.6%) received Bortezomib-based schemes as part of the first line. Two hundred and fifty-two patients (28.3%) were consolidated with Autologous Stem Cell Transplantation (ASCT) in first-line. ASCT consolidation and age were the main independent factors influencing outcomes; in the non-ASCT cohort, 5-year overall survival was 48.7% (CI 41.8-55.2) compared to 80.7% (CI 73-86.4) in ASCT patients. CONCLUSION: This data depicts the reality of MM in Colombia, which likely reflects other Latin American countries, where access barriers to diagnosis and treatment are echoed in advanced stage diagnosis and a low rate of transplants. These seem to negatively impact survival despite the availability of most novel drugs approved for this disease. Thus, emphasizing the paradox that prevails in most of the region: availability without equitable access.
Asunto(s)
Trasplante de Células Madre Hematopoyéticas , Mieloma Múltiple , Anciano , Bortezomib/uso terapéutico , Colombia/epidemiología , Femenino , Humanos , Masculino , Mieloma Múltiple/diagnóstico , Mieloma Múltiple/epidemiología , Mieloma Múltiple/terapia , Estudios Prospectivos , Sistema de Registros , Estudios Retrospectivos , Trasplante AutólogoRESUMEN
Oxaliplatin is a chemotherapeutic agent with direct toxic action on deoxyribonucleic acid (DNA), which is known to cause an arrest in its synthesis and inducing cell death. It is a crucial medication for colorectal carcinoma, and in combination with other medications has demonstrated to exhibit synergism, managing to increase patients' survival, especially when compared to monotherapy with 5-fluoracil. Neurotoxicity is its most well-known adverse effect. However, other less frequent secondary effects have been described in case reports, among them liver injury, which is usually secondary to liver sinusoid injury. Despite the wide frequency of the use of this drug, the relationship of oxaliplatin with the development of portal non-cirrhotic hypertension is largely unknown, which translates into a sub-diagnosis, representing an additional risk to patients who develop this complication. We present the case of an adult patient, who during treatment with the FOLFOX scheme for colorectal carcinoma, presents signs suggestive of portal hypertension, without other risk factors besides the administration of oxaliplatin.
RESUMEN
Given the benefits and likely future applications, there is an urgent need to expand the use of next-generation sequencing (NGS) in breast, lung, and unknown primary cancers in Colombia. The objective of this review is to address the barriers limiting access to the use of NGS in Colombia, specifically for patients with breast, lung, and unknown primary cancers in the public health care system. A selected Panel of Colombian experts in NGS were provided with a series of relevant questions to address in a multiday conference. Each narrative was discussed and edited by the Panel through numerous drafts and rounds of discussion until consensus was achieved. There are limitations to the widespread adoption of innovative technology inherent to the Colombian health care system. Barriers identified to implementing NGS in Colombia include availability, accessibility, and affordability; limited infrastructure; training and awareness of health personnel; quality-control procedures; and collection of local data. Stakeholders must align to adapt the implementation of NGS to the constraints of resource-limited environments. Diagnostic algorithms were developed to guide molecular testing for lung, breast, and unknown primary cancers. Recommendations on overcoming the barriers to the widespread adoption of NGS include country-specific molecular testing guidelines, creating a national genetic registry, improving infrastructure, and creating health policy that favors the adoption of innovative technology.
Asunto(s)
Neoplasias Primarias Desconocidas , Colombia , Consenso , Secuenciación de Nucleótidos de Alto Rendimiento , Humanos , PulmónRESUMEN
INTRODUCTION: The ACHOCC-19 study was performed to characterize COVID-19 infection in a Colombian oncological population. METHODOLOGY: Analytical cohort study of patients with cancer and COVID-19 infection in Colombia. From April 1 to October 31, 2020. Demographic and clinical variables related to cancer and COVID-19 infection were collected. The primary outcome was 30-day mortality from all causes. The association between the outcome and the prognostic variables was analyzed using logistic regression models and survival analysis with Cox regression. RESULTS: The study included 742 patients; 72% were >51 years. The most prevalent neoplasms were breast (132, 17.77%), colorectal (92, 12.34%), and prostate (81, 10.9%). Two hundred twenty (29.6%) patients were asymptomatic and 96 (26.3%) died. In the bivariate descriptive analysis, higher mortality occurred in patients who were >70 years, patients with lung cancer, ≥2 comorbidities, former smokers, receiving antibiotics, corticosteroids, and anticoagulants, residents of rural areas, low socioeconomic status, and increased acute-phase reactants. In the logistic regression analysis, higher mortality was associated with Eastern Cooperative Oncology Group performance status (ECOG PS) 3 (odds ratio [OR] 28.67; 95% confidence interval [CI], 8.2-99.6); ECOG PS 4 (OR 20.89; 95% CI, 3.36-129.7); two complications from COVID-19 (OR 5.3; 95% CI, 1.50-18.1); and cancer in progression (OR 2.08; 95% CI, 1.01-4.27). In the Cox regression analysis, the statistically significant hazard ratios (HR) were metastatic disease (HR 1.58; 95% CI, 1.16-2.16), cancer in progression (HR 1.08; 95% CI, 1.24-2.61) cancer in partial response (HR 0.31; 95% CI, 0.11-0.88), use of steroids (HR 1.44; 95% CI, 1.01-2.06), and use of antibiotics (HR 2.11; 95% CI, 1.47-2.95). CONCLUSION: In our study, patients with cancer have higher mortality due to COVID-19 infection if they have active cancer, metastatic or progressive cancer, ECOG PS >2, and low socioeconomic status. IMPLICATIONS FOR PRACTICE: This study's findings raise the need to carefully evaluate patients with metastatic cancer, in progression, and with impaired Eastern Cooperative Oncology Group status to define the relevance of cancer treatment during the pandemic, consider the risk/benefit of the interventions, and establish clear and complete communication with the patients and their families about the risk of complications. There is also the importance of offering additional support to patients with low income and residence in rural areas so that they can have more support during cancer treatment.
Asunto(s)
COVID-19 , Neoplasias Pulmonares , Estudios de Cohortes , Humanos , América Latina , Neoplasias Pulmonares/complicaciones , Neoplasias Pulmonares/tratamiento farmacológico , Neoplasias Pulmonares/epidemiología , Masculino , SARS-CoV-2RESUMEN
PURPOSE: Limited information is available on multiple myeloma (MM), chronic lymphocytic leukemia (CLL), and non-Hodgkin lymphoma (NHL) management in Latin America. The primary objective of the Hemato-Oncology Latin America (HOLA) study was to describe patient characteristics and treatment patterns of Latin American patients with MM, CLL, and NHL. METHODS: This study was a multicenter, retrospective, medical chart review of patients with MM, CLL, and NHL in Latin America identified between January 1, 2006, and December 31, 2015. Included were adults with at least 1 year of follow-up (except in cases of death within 1 year of diagnosis) treated at 30 oncology hospitals (Argentina, 5; Brazil, 9; Chile, 1; Colombia, 5; Mexico, 6; Panama/Guatemala, 4). RESULTS: Of 5,140 patients, 2,967 (57.7%) had NHL, 1,518 (29.5%) MM, and 655 (12.7%) CLL. Median follow-up was 2.2 years for MM, 3.0 years for CLL, and 2.2 years for NHL, and approximately 26% died during the study observation period. Most patients had at least one comorbidity at diagnosis. The most frequent induction regimen was thalidomide-based chemotherapy for MM and chlorambucil with or without prednisone for CLL. Most patients with NHL had diffuse large B-cell lymphoma (DLBCL; 49.1%) or follicular lymphoma (FL; 19.5%). The majority of patients with DLBCL or FL received rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone. CONCLUSION: The HOLA study generated an unprecedented level of high-quality, real-world evidence on characteristics and treatment patterns of patients with hematologic malignancies. Regional disparities in patient characteristics may reflect differences in ethnoracial identity and level of access to care. These data provide needed real-world evidence to understand the disease landscape in Latin America and may be used to inform clinical and health policy decision making.
Asunto(s)
Leucemia Linfocítica Crónica de Células B/epidemiología , Linfoma no Hodgkin/epidemiología , Mieloma Múltiple/epidemiología , Adulto , Anciano , Anciano de 80 o más Años , Humanos , América Latina/epidemiología , Persona de Mediana Edad , Sistema de Registros , Adulto JovenRESUMEN
SETDB1 is a key histone lysine methyltransferase involved in gene silencing. The SETDB1 gene is amplified in human lung cancer, where the protein plays a driver role. Here, we investigated the clinical significance of SETDB1 expression in the two major forms of human non-small cell lung carcinoma (NSCLC), i.e., adenocarcinoma (ADC) and squamous cell carcinoma (SCC), by combining a meta-analysis of transcriptomic datasets and a systematic review of the literature. A total of 1140 NSCLC patients and 952 controls were included in the association analyses. Our data revealed higher levels of SETDB1 mRNA in ADC (standardized mean difference, SMD: 0.88; 95% confidence interval, CI: 0.73-1.02; p < 0.001) and SCC (SMD: 0.40; 95% CI: 0.13-0.66; p = 0.003) compared to non-cancerous tissues. For clinicopathological analyses, 2533 ADC and 903 SCC patients were included. Interestingly, SETDB1 mRNA level was increased in NSCLC patients who were current smokers compared to non-smokers (SMD: 0.26; 95% CI: 0.08-0.44; p = 0.004), and when comparing former smokers and non-smokers (p = 0.009). Furthermore, the area under the curve (AUC) given by the summary receiver operator characteristic curve (sROC) was 0.774 (Q = 0.713). Together, our findings suggest a strong foundation for further research to evaluate SETDB1 as a diagnostic biomarker and/or its potential use as a therapeutic target in NSCLC.
RESUMEN
Se describe la obtención, purificación y caracterización de dos proteínas hipofisiarias de origen caprino con carga eléctrica diferente y con características de hormona luteinizante (LH). La fracción no retenida en la cromatografía de intercambio catiónico (CM-celulosa) designada CM-lab y la correspondiente al segundo pico de dicha cromatografía (CM-2ab), se repurificaron en una cromatografía de intercambio aniónico (DEAE-celulosa) en condiciones idénticas, para obtener LH-I (CM-lab-DEAE-la) con un rendimiento de 76 mg/kg de adenohipófisis, y a la LH-II (CM2ab-DEAE-lb) con 15 mg/kg. La diferencia de carga de cada proteína se determinó por su movilidad relativa (Rf) mediante una electroforesis en geles de poliacrilamida (PAGE) en condiciones nativas. La LH-I mostró un Rf de 0.09 (banda mayoritaria) y 0.415, mientras la LH-II presentó 2 bandas de tipo catiónico con un Rf de 0.14, 0.19 (banda mayoritaria). La determinación del peso molecular relativo de LH-I y LH-II, se llevo a cabo por medio de una electroforesis en geles de poliacilamida-dodecilsulfato de sodio (SDS-PAGE). En condiciones no reductoras (NR), ambas proteínas presentaron un peso molecular relativo de 36.5 kilodaltones (KDa) correspondiente a la forma monomérica, semejante a los estándares NIDDK-oLH-26 y USDA-bLH5, mientras que en presencia de 2ß-mercaptoetanol (condiciones reducidas), las proteínas presentaron un peso molecular de 22.4 y 20.2 KDa. El análisis por inmunotransferencia (Western-blot) en condiciones NR utilizando el anti-oLH (CSU-204), permitió identificar bandas inmunorreactivas de peso molecular de 50,43, 36.5 (mayoritaria), y 22.4 KDa, tanto en los estándares como en las fracciones obtenidas en este estudio. La potencia biológica realizada en un bioensayo in vivo 3 + 3 balanceado fue de 1.03 UI/mg para la LH-I. y de 0.65 UI/mg para la LH-II con intervalos de confianza de 95 por ciento. Su actividad inmunológica se determinó con un radioinmunoensayo (RIA) homólogo de LH caprina, a la dosis esperada del 50 por ciento (ED 50). Los resultados fueron de 1.7 ng/ml y 3.5 ng/ml para LH-I y LH-II respectivamante. Se concluye que esta técnica permite la obtención de dos proteínas con carga eléctrica diferente, con actividad biológica e inmunológica de LH, y con peso molecular idéntico