The diagnosis of breast cancer during pregnancy presents various complexities for patients and practitioners since the benefit of the woman’s treatment must be compatible with the well-being of the foetus. Cancer diagnosed during pregnancy is rare, occurring in 2.3 cases out of every 100,000, however, this figure has progressively grown over recent years as women are becoming mothers at an increasingly older age. Twenty years ago therefore, the number of women that became pregnant at the age of 35 accounted for 35%, while today in Spain it is the average age that women have their first child. In 2006, a protocol was established at the Breast Cancer Unit, the Vall d’Hebron University Hospital, to treat women in a holistic manner involving a multidisciplinary team comprising gynaecologists, obstetricians, foetal medicine specialists, oncologists, specialized surgeons in breast cancer, and paediatricians. This integrated approach facilitates communication between the experts involved in decision-making as well as enhances the safety, flexibility and effectiveness of the management of these pregnant patients during treatment. The ultimate goal of this task force is to ensure the utmost safety and effectiveness for the mother without harming the development of the foetus. Patients that have been diagnosed with breast cancer during pregnancy have the option of either interruption or continuation of the pregnancy. Until now, many women have previously chosen the former because they were not offered an alternative. At the Vall d’Hebron University Hospital however, since this protocol was established, women are duly informed about the possibility of continuing the pregnancy and receiving the most appropriate treatment at the same time. Importantly, these patients require highly comprehensive monitoring starting at diagnosis, at which point the multidisciplinary team defines the best strategy to follow considering the stage of pregnancy and as well as that of the tumour. In accordance with this, a decision is made regarding initiating treatment with chemotherapy or surgery and timelines for treatment are established to achieve the maximum effectiveness for the mother and the safest treatment for the foetus. Thereafter, a circuit is established whereby each time the patient is to receive chemotherapy, a prior analysis and ultrasound of the foetus are carried out in addition to a check-up with the obstetrician and the oncologist to ensure the proper development of the foetus. The patient may then receive chemotherapy that same day. This monitoring is essential to control the development of the patient’s cancer and that of the pregnancy at all times. The key to the success of this programme is team-work as well as experience accumulated over the years in addressing the challenge of treating breast cancer during pregnancy. Furthermore, over recent years, advances have been successfully integrated into the treatment of these patients such as selective sentinel lymph node biopsy, taxane-based chemotherapy and foetal echocardiography, among others, which have led to comparable results to patients that are not pregnant, without harming the foetus. The experience accumulated in this field has also allowed the medical team responsible for this protocol to develop research projects aimed at improved outcomes for patients. Research focuses on the various effects chemotherapy may have on the foetus. In addition, the Vall d’Hebron Hospital collaborates with international groups also working on cancer and pregnancy to continue to improve protocols. At Vall d´Hebron the patient is centered at the core of all research programs from the translational and preclinical levels to the clinic. Our research consequently aims at discovering the factors and mechanisms driving tumoral progression to obtain more accurate prognosis, tailored diagnosis and ultimately personalized treatment for breast cancer patients. "This is facilitated not only through direct access to patients and tumor samples but also through the planned connectivity between basic, translational researchers and clinicians working as teams implicated in the various research projects, " explains Dr. Joaquín Arribas, Director of Preclinical Research at the Vall d´Hebron Institute of Oncology (VHIO). The type of research conducted al Vall d’Hebron can be exemplified by the case of HER2-positive breast cancers for, accounting for between 15 - 20% of all cases. Much progress in combating this tumor type has been made thanks to drugs directed against HER2 such as trastuzumab, pertuzumab, lapatinib, or T-DM1. Despite the undeniable success of these therapies, sadly, many tumors ultimately develop resistance against them. Groups at Vall d’Hebron are currently tackling this problem to optimize these therapies. To solve these remaining questions behind such resistance and given the immense challenges arising from cancer heterogeneity, research at Vall d´Hebron is basic-applied, adopting a purely translational approach. At molecular level, thanks to the development of xenograft models with explant tumors from patients in mice in order to mimic the patient´s disease and study tumor development in optimized research models, the detection of mutations and mechanisms of resistance to current therapies associated with the disease is both facilitated and accelerated.