RESUMEN Introduccion . El papel de la biopsia del ganglio centinela realizada despues de quimioterapia neoadyuvante es controvertido. El objetivo del presente estudio es analizar el valor del ganglio centinela en los tumores de mama avanzados que han recibido neoadyuvancia y estudiarlos con tecnicas de hematoxilina y eosina, inmunohistoquimica y molecular de reaccion en cadena de la polimerasa (RT-PCR). Material y metodos. Un total de 33 pacientes fueron incluidos en el estudio; estos enfermos recibieron neoadyuvancia y se les realizo la tecnica del ganglio centinela. Una vez extraido el ga nglio, este era enviado a anatomia patologica, donde era evaluado y posteriormente se fragmentaba, utilizando entre un 25% y 50% del ganglio para el estudio en el laboratorio de biologia molecular. Resultados. Los ganglios centinelas se estudiaron con las tecnicas de hematoxilina y eosina, inmunohistoquimica y la molecular, encontrando un incremento de la sensibilidad con la ultima tecnica, la del RT-PCR. Los ganglios centinelas fueron negativos en un 45.1% y las linfadenectomias fueron negativas en un 61.3% despues de neoadyuvancia. Las recidivas locales a 5 anos equivalen al 8.3%. Para nuestra serie la tasa de sobrevida libre de enfermedad a 5 anos en estadio II es del 100% y en estadio III es del 87.5%. Conclusion . Existe un escaso numero de pacientes estudiadas, sin un seguimiento que avale el uso de la biopsia del ganglio centinela despues de neoadyuvancia, por lo que actualmente solo debiera realizarse con fines de investigacion. Al comparar las tecnicas de hematoxilina y eosina, inmunohistoquimica y molecular, comprobamos mayor sensibilidad en la tecnica molecular, lo cual permite disminuir los falsos negativos y tener un mejor diagnostico de las metastasis en los ganglios centinela. Palabra clave: Tecnica del ganglio centinela, carcinoma de mama avanzado, estudio molecular RT-PCR. ABSTRACT A COMPARISON BETWEEN DIFFERENT SENTINEL NODE DETECTION TECHNIQUES AFTER NEOADJUVANCY IN BREAST CANCER Introduction. Since the role of sentinel node biopsy after neoadjuvant chemotherapy is controversial, the aim of our study was to analyze the value of sentinel node detection in advanced breast tumors that received neoadjuvant therapy. Technical study was done with hematoxylin/eosin stain, immunohistochemistry and molecular polymerase chain reaction (RT-PCR). Material and methods: We studied 33 patients who received neoadjuvant therapy and underwent sentinel node procedure. After removing the node, it was sent to pathology where it was evaluated; further fragments, using between 25% and 50% of the lymph node, were used for analysis at the molecular biology laboratory. Results : The sentinel nodes were studied with hematoxylin and eosin, immunohistochemistry and molecular techniques, finding an increase in sensitivity with RT-PCR. They were negative in 45.1% and lymphadenectomy tissue was negative in 61.3% after neoadjuvant therapy. Local recurrences at 5 years are equivalent to 8.3%. For our series the rate of disease-free survival at 5 years in stage II is 100% and stage III is 87.5%. Conclusion. Sentinel node biopsy after neoadjuvant therapy for breast cancer should only be a matter of research, since the number of studied patients is small and there have been no monitoring to endorse a wide use of the procedure. When comparing hematoxylin/eosin, immunohistochemistry and molecular techniques, increased sensitivity was found with the molecular one; RT-PCR can reduce false negative reports and furnish a better diagnosis of sentinel node metastases. Key words : Sentinel node technique, advanced breast cancer, molecular study RT-PCR.