eP112 Collision tumour with features of primary lung and metastatic breast cancer: first reported case in the United Kingdom

Introduction Collision tumour consists of two histologically different tumours that develop independently but intermix with one another. Three previous cases of primary lung and metastatic breast collision tumour have been described in the literature. We report the UKs first such case. Case presentation A 63-year-old female presented with an incidental 21mm spiculated right lung nodule on a CT scan. Two subsequent CT-guided lung biopsies were non-diagnostic. Whole body FDG-PET showed the lesion to be suspicious for malignancy, with no other suspicious areas. Initial treatment consisted of a right lung middle lobe lobectomy. Final pathology demonstrated a collision tumour: primary lung adenocarcinoma mixed with metastatic triple negative invasive breast ductal carcinoma (pT1bpN2pM0). Due to positive pulmunory lymph node the patient has been recommended adjuvant chemotherapy (carboplatin and vinorelbine). Remarkably, no breast primary cancer or abnormal axillary lymph nodes have been detected in this patient, with normal clinical examination, mammograms and breast MRI. Given no breast primary it was breast MDT consensus that there is no obvious gain from breast specific immuno-chemotherapy or radiotherapy. The patient will undergo yearly clinical examination and surveillance mammograms for five years. Conclusion This is a rare case of a collision tumour comprising of a primary lung adenocarcinoma mixed with metastatic triple negative invasive ductal breast carcinoma. The lack of standardised guidelines on this topic pose a treatment dilemma. As such, we recommend a combined breast and lung MDT discussion with the merit of adjuvant chemotherapy, radiotherapy and endocrine therapy based on the final tumour pathology.