Given the increasing complexity of cancer care, multidisciplinary tumor boards have become essential in daily clinical oncology practice. The Project Extension for Community Healthcare Outcomes (ECHO) initiative developed an innovative telementoring model using a "hub and spoke" design consisting of a team of experts (hub) that offers a full service to multiple participants (the spokes) during regularly scheduled sessions discussing patients' clinical cases. The Alexander Fleming Cancer Institute in Buenos Aires was the first hub in Latin America to implement Project ECHO for gastrointestinal tumors. In our 3-year experience, 80 patients from 37 centers were evaluated within Project ECHO and a range of three to five cases were discussed in each meeting. From our perspective, the impact of this novel approach was a remarkable strategy to reduce care disparities by equalizing access to high-quality medical knowledge in a multidisciplinary environment for medical discussions. Additionally, it was shown to have a cost-effective impact directly on the patients and the local health system, since relevant costs were saved after unnecessary treatments, studies and travel expenses were avoided.

146 Background: Short-course radiotherapy (SCRT) is an option in the neoadjuvant setting of resectable stage II-III rectal cancer, as well as in stage IV disease for local control without delay to initiate systemic treatment. Short-course radiotherapy is reported to be a comparable strategy for locally advanced rectal cancer. Limited data exist regarding the use of short-course radiation therapy when used as part of a non-surgical watch and wait approach. Methods: This is a retrospective analysis of all patients that underwent SCRT for rectal cancer at the Alexander Fleming Institute from 3/2014 to 6/2022. Results: 44 patients were treated with SCRT, 29 (66%) were male, with a median age of 59 years (46-73). Most of the patients had stage IV disease (26, 59,1%) followed by clinical stage II-III (18, 40,9%). 30 (68%) were localized in the middle with 14 (32%) in the lower rectum, by MRI imaging. In locally advanced disease 5/18 had T4 disease and 7/18 had N≥2. 14/18 patients (89%) underwent SCRT followed by consolidation chemotherapy (ChT) and 4 (11%) had induction ChT followed by SCRT. In metastatic disease 14/26 patients (53.84%) underwent SCRT followed by consolidation ChT, 10 (38.46%) had induction ChT followed by SCRT, and 2 (7.7%) received only SCRT. 29 (65.9%) of patients underwent surgery. 17/29(58.6%) had metastatic disease and 12/29 (41.4%) had locally advanced disease. Pathological response rates in operated patients were 2 (6.9%). 8 (18.2%) cases had a clinical complete response (cCR) (n=6 stage II-III and n=2 stage IV). Five (27.7% of the locally advanced group) patients with cCR underwent watch and wait with 1 local recurrence after 14 months. The remainder is disease free with a median follow-up time of 20 months (IC 95%: 15.14-24.85). Those that underwent SCRT following chemotherapy were more likely to have AEs compared to those that had chemotherapy following SCRT (11/30, 36.7% vs 25%, p=0.02). Conclusions: Our work shows that in a subgroup of patients diagnosed with LARC treated with SCRT followed by Chemotherapy, surgical treatment could be deferred after achieving a complete clinical response. The shorter time involved by SCRT allowed for less treatments with similar toxicity to long-course treatment regimens. SCRT is a reasonable option for local disease control in stage IV disease.

La evaluación de cfDNA (cell-free DNA) en biopsia líquida en cáncer de colon metastásico (CCRm), tiene alta sensibilidad/especificidad y concordancia con la biopsia del tejido para evaluar mutaciones de novo o resistencia a la terapia dirigida.El objetivo fue analizar la frecuencia de mutaciones RAS/ BRAF en cfDNA de pacientes con CCRm. Este es un estudio retrospectivo, descriptivo y observacional de pacientes con CCRm que realizaron biopsia líquida en el Instituto Alexander Fleming desde 02/2020 hasta 11/2020. Se analizaron 41 pacientes, 54% (22) eran de sexo masculino. La edad mediana fue de 52 años (r 45- 61). Se diagnosticaron en estadio IV 66% (27), III 12% (5), II 17% (7) y I 5% (2). La localización del primario fue izquierda en 78% (32) de los pacientes. El sitio metastásico más frecuente fue hepático en 76% (31/41) de los cuales se presentaron en forma sincrónica en 87% (27) de los casos. La presentación en más de dos sitios metastásicos fue de 9% (23). Las mutaciones KRAS/BRAF se observaron en 51% (21) de los pacientes. Se solicitó cfDNA en primera o segunda línea en 63% (26) y en tercera o más en 37% (15) de los casos. El 37% (15) de los pacientes a los que se les solicitó en tercera o más líneas cfDNA se obtuvieron resultados de RAS/BRAF mutado en 47% (7) y RAS/BRAF no mutado en 53% (8). Los esquemas más utilizados en este escenario fueron quimioterapia ± bevacizumab 53% (8), anti- EGFR más quimioterapia 20% (3), trifluridine/ tipiracil o regorafenib 20% (3) e inmunoterapia 7% (1). El 38% (3/8) con KRAS/BRAF no mutado realizaron reintroducción con anti-EGFR. Con un seguimiento mediano de 9 meses (IC 95% 8,1-9,8), la supervivencia libre de progresión (SLP) para los pacientes KRAS/BRAF no mutados y mutados fue de 11 (IC 95% 6 – NA) y 5 (IC 95% 4 – NA) meses respectivamente. Concluimos que en nuestra experiencia, la biopsia líquida fue útil tanto en primera como en tercera línea para demostrar la presencia de mutaciones RAS/BRAF en el 51% de los pacientes con CCRm.

Background: Short-course radiotherapy (SCRT) of 25 Gy in five daily fractions is a recommended strategy in the neoadjuvant setting for resectable locally advanced rectal cancer (LARC), as well as in cases of metastatic disease for local control. There is scarce information regarding the use of SCRT for patients who have received nonoperative management.Objectives: To describe the characteristics of patients who received treatment with SCRT for LARC and metastatic rectal cancer, toxicity, and the approach after radiation treatment.Methods: This is a retrospective analysis of all patients who underwent SCRT for rectal cancer at the Alexander Fleming Institute from March 2014 to June 2022. Results:In total, 44 patients were treated with SCRT. The majority were male (29, 66%), with a median age of 59 years (interquartile range 46-73). Most patients had stage IV disease (26, 59.1%), followed by LARC (18, 40.9%). Most lesions were located in the middle rectum (30, 68%). The majority of LARC patients underwent SCRT followed by consolidation chemotherapy (ChT) (16/18, 89%), while most patients with metastatic disease underwent SCRT followed by consolidation ChT (14/26, 53.8%). A clinical complete response (cCR) was documented in 8/44, 18.2% of patients. Most patients with LARC and cCR were managed by a watch and wait approach (5/18, 27.7%). Local recurrence was observed in LARC cases (2/18, 11.1%). Patients who underwent SCRT following consolidation ChT were more likely to have adverse events (AEs) than those undergoing induction ChT following SCRT (11/30, 36.7% versus 3/12, 25%, p = 0.02) Conclusion:In a subgroup of patients diagnosed with LARC and treated with SCRT followed by ChT, surgical treatment could be omitted after they achieved a cCR. Local recurrence was similar to that reported in a previous study. SCRT is a reasonable option for local disease control in stage IV disease, yielding low toxicity rates. Therefore, decisions must be made by a multidisciplinary team. Prospective studies are necessary to reach further conclusions.

Background Immunotherapy is the first-line treatment in patients with advanced microsatellite instability-high (MSI-H) or deficient mismatch repair (dMMR) colorectal cancer (CRC). Although immune checkpoint inhibitors (ICIs) for locally advanced rectal cancer (LARC) are not yet a standard, the results are very encouraging and raise the question of whether patients with clinical complete response (cCR) could receive nonoperative management (NOM). However, different patterns of response have challenged management strategies. Case Description A 34-year-old woman diagnosed with dMMR LARC started treatment with capecitabine 2,000 mg/m 2 on day 1 to 14 and oxaliplatin 130 mg/m 2 on day 1 and every 21 days. Magnetic resonance imaging (MRI), performed three cycles later, showed local progression of the primary rectal lesion, which at that time had new peritoneal reflex involvement. A new hepatic lesion in segment V was observed. Due to disease progression, she was administered pembrolizumab 200 mg every 21 days. After three cycles, a discordant radiological response was observed on a new MRI scan that showed a complete response of the liver lesion and magnetic resonance tumor regression grade (mrTRG) 1 in the rectum. However, new involvement of the mesentery and enlargement of the regional lymph nodes (LNs) were also evident. A new colonoscopic biopsy was performed, showing no cancerous cells. She underwent surgery on the rectum and liver lesion. Pathology showed a complete response of the rectal wall and liver lesion, but 1 of 22 LNs was positive for adenocarcinoma (ypT0 N1 M0). The patient continued on pembrolizumab, and 14 months after surgery, she had not relapsed. Conclusions Neoadjuvant immunotherapy for rectal cancer requires new recommendations for the assessment of clinical response. Pseudoprogression should be ruled out as an atypical response before deciding on surgical treatment. We propose an algorithm to address pseudoprogression in this setting.