Background: Breast cancer is one of the most common malignant forms of neoplasia worldwide; programmed death protein 1 (PD-1), an inhibitory receptor of T lymphocytes, and its ligand programmed death ligand 1 (PD-L1), play an important role in the ability of tumor cells to evade the host's immune system. Methods:We conducted a descriptive, observational study using retrospective data and an open evaluation using immunohistochemistry to determine the general prevalence of PD-L1 expression in 63 women with breast cancer who underwent a modified radical mastectomy, or quadrantectomy, with axillary lymph node removal. Results:The prevalence of PD-L1 expression was 32% in patients with breast cancer treated with radical mastectomy. PD-L1 expression was higher in patients with large tumor size (19% for pT1, 37% for pT2, 50% for pT3, and 100% for pT4), metastasis in regional lymph nodes (25% for N0, 38% for N1, 75% for pN2, and 38% for pN3), and higher histological grade carcinoma (0% for grade 1, 23% for grade 2, and 50% for grade 3).Conclusions: These findings suggest that PD-L1 expression is heterogeneous in breast cancer tumors and that its expression varies highly in tumor regions over time. The evaluation of PD-L1 expression is significant, because of the therapeutical implications that could improve the outcomes and prognosis of these patients.

e22505 Background: Knowledge and awareness of cancer screening among medical doctors has a great relevance in prevention of oncologic diseases. It is well known that cancer screening can significantly improve patients’ outcomes and prognosis by reducing morbidity and mortality rates. Therefore, improving medical doctors’ knowledge regarding cancer screening can directly influence health promotion behavior as well as their capacity to recognize cancer in premalignant or early stages of the disease. The aim of this study was to assess the level of knowledge of cancer screening among medical students and doctors. Methods: In this cross-sectional study we evaluated the cancer screening knowledge of medical students and physicians residing in Puebla City, Mexico. This study was conducted by the Centro Oncológico Integral at the Hospital Ángeles de Puebla in Puebla, Mexico. All the participants had given their informed consent for the use of their data for research purposes. Data was collected using an anonymous online-based, pre-tested, self-administered questionnaire to measure their knowledge about cervical, breast, lung, colon and prostate cancer screening. Data analysis was done using R-Statistics. Results: A total of 383 health care professionals were included in the study. The mean age of the participants was 28 years. Participants included last year medical students (n = 68, 17.8%), interns (n = 37, 9.7%), social service year physicians (n = 75, 19.6%), general practitioners (n = 138, 36%), residents (n = 23, 6%) and specialists (n = 42, 11%). The questionnaire consisted of 20 questions, the total knowledge score had a quartile 1 (Q1) of 11 points, a quartile 2 (Q2) of 13 points and a quartile 3 (Q3) of 14 points. Participants were categorized in three groups according to their score: 45.95% showed a low (< Q2) level of knowledge, 30.02% a moderate (Q2–Q3) level of knowledge and only 24.02% a high (> Q3) level of knowledge. Residents and specialists showed a better median score than other groups of participants. A one-way ANOVA revealed that there was a statistically significant difference in the level of knowledge according to the occupation of the participants (p = 0.0171). Conclusions: Most participants showed a low to moderate level of knowledge about cancer screening in this study. Active measurements, effective education programs and communication strategies are required to improve the level of knowledge and awareness of health care professionals in cancer screening and prevention.