A 52-year-old woman has a large pericardial effusion attributed to malignancy. Which primary cancer is most commonly associated with this finding?

The association between malignancy and pericardial effusion is particularly strong with breast cancer. This is due to several factors, including the propensity of breast cancer to metastasize to the pleura and pericardium, leading to fluid accumulation in these spaces. Breast cancer can also lead to lymphatic obstruction or direct invasion of the pericardium, which can precipitate the development of a pericardial effusion.

While other cancers may also be associated with pericardial effusions, breast cancer has been extensively studied and documented as one of the most frequent primary tumors leading to this complication. The likelihood of pericardial effusion increases in patients who have advanced or metastatic breast cancer, highlighting its significant relevance in clinical practice.

This aligns with the observation that when evaluating a patient with a large pericardial effusion, especially in cases where malignancy is suspected, breast cancer should be considered as a primary source.