PURPOSE: The integration of novel systemic therapies including antibody-drug conjugates (ADCs), immune checkpoint inhibitors (ICIs), and cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors with radiotherapy (RT) presents new opportunities in breast cancer (BC) management. However, clinical guidance on concurrent administration remains limited, particularly for advanced techniques. MATERIALS AND METHODS: A multidisciplinary panel of radiation and medical oncologists from AROME and the Moroccan Medical Oncology Association conducted a literature review and established expert consensus recommendations during the fourth Moroccan Congress of Medical Oncology Private Practice. An evidence-informed, structured consensus process was used to achieve agreement on safety profiles across six RT modalities. RESULTS: Trastuzumab deruxtecan has shown a favorable safety profile with whole-breast irradiation and palliative RT, while trastuzumab emtansine combined with stereotactic radiosurgery shows elevated radionecrosis risk. ICIs are generally feasible with most RT modalities and toxicity monitoring applied; however, risk is context dependent, and evidence supporting stereotactic body radiotherapy-ICI benefit in oligometastatic BC remains limited. The use of CDK4/6 inhibitors concurrently with conventional and stereotactic RT seems feasible, although caution is advised for visceral metastases. These experts' agreements are supported by retrospective data and preclinical evidence, highlighting the need for prospective validation. CONCLUSION: This expert consensus statement provides pragmatic, modality-specific guidance on combining contemporary RT techniques with selected novel systemic agents in BC, complementing existing European Society for Medical Oncology /European Society for Radiotherapy and Oncology‑oriented frameworks and highlighting areas where prospective data are still needed. The findings underscore the importance of toxicity monitoring, particularly for ADCs in CNS-directed therapies, and call for biomarker-driven studies to optimize combination strategies. These recommendations aim to guide safe integration of novel agents with RT across resource-variable settings, including low- and middle-income countries.

Peritoneal metastasis (PM, or peritoneal carcinomatosis) is often associated with dismal prognosis. The treatment of peritoneal metastasis depends on several factors, including the type of primary cancer, the extent of metastasis and the patient’s overall health condition. Apart from systemic chemotherapy and cytoreductive surgery (CRS), locoregional therapies such as hyperthermic intraperitoneal chemotherapy (HIPEC) or pressurized intraperitoneal aerosol chemotherapy (PIPAC) may improve tumour control. CRS is a complex procedure with high morbidity, performed only in approximately 25% of all eligible patients and the efficiency of other non-surgical therapies is not well known. The place of radiation therapy needs to be defined. A 62-year-old woman was referred for surgery for a few days’ history of large bowel obstruction. A previous abdominopelvic CT showed an obstructive 3-cm mass in the proximal ascending colon, associated with small bowel dilatation. Right hemi-colectomy was performed. Work-up demonstrated on MRI (magnetic resonance imaging) sub-centimetric secondary liver lesions. 18F-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) ruled out other metastatic lesions. After multidisciplinary discussion, peri-operative systemic therapy based on FOLFOX-Bevacizumab was offered and was associated with stable disease for 7 months. Unfortunately, peritoneal progression was detected on PET/CT imaging. FOLFIRI-Bevacizumab was offered as second line systemic therapy followed by resection of residual masses. The patient was considered in remission for 5 months thereafter. A second isolated peritoneal relapse occurred involving the same 2 distinct sites. Second line chemotherapy was re-challenged. The oligorecurrent PM lesions were considered as non-operable. After multidisciplinary team discussion, stereotactic body radiation therapy (SBRT) was decided. The relapse sites were treated with 48 Gy, delivered in 6 fractions of 8 Gy given every other day. At the 22-month follow-up, the patient showed no signs of relapse on CT imaging and no treatment-related toxicities. Isolated peritoneal oligometastatic metastases are associated with poor prognosis. Cytoreductive surgery remains the historical standard of care treatment but represents a minority of all eligible patients. Our case and few other reports suggest that SBRT is a safe, reasonable, and non-invasive treatment option.