Mastitis is the inflammation of breast tissue. From a pathophysiological point of view, mastitis reflects a variety of underlying etiologies. It can be due to non-infectious inflammation, infection (generally of bacterial origin) but can also be caused by inflammation resulting from malignant tumor growth. Mastitis always manifests clinically by three cardinal signs of inflammation, which are redness, heat and pain. Breast specialists examining women with mastitis should proceed as follows: first, it is important to distinguish between cancer-related and non-cancer-related breast inflammation, since their clinical presentation can be misleading. Cancer-related mastitis reflecting the presence of aggressive cancer is less commonly observed than other forms of mastitis but its diagnosis, which can sometimes be difficult, needs to be made, or excluded, without delay. Once cancer-related mastitis has been excluded, the causes of inflammation should be elucidated to enable rapid treatment and patient recovery.