Which type of breast cancer is associated with the worst prognosis?

Triple-negative breast cancer is associated with the worst prognosis primarily due to its distinct biological characteristics and treatment challenges. This type of breast cancer is defined by the absence of three key receptors: estrogen, progesterone, and human epidermal growth factor receptor 2 (HER2). Because these receptors are not present, patients do not benefit from hormone therapies or targeted treatments that are effective for other breast cancer subtypes.

Additionally, triple-negative breast cancer tends to be more aggressive, often presenting at a higher grade and with a greater likelihood of metastasis at diagnosis compared to other types. This subtype is also more prevalent in younger women and tends to exhibit a higher rate of recurrence, particularly within the first few years following initial treatment.

Hormonal receptor-positive breast cancer and HER2-positive breast cancer generally have better prognoses due to the availability of targeted therapies, such as hormone therapies for the former and HER2 inhibitors for the latter. Invasive lobular carcinoma has a somewhat different biological behavior but also tends to be associated with a better overall prognosis compared to triple-negative breast cancer, especially when detected at an earlier stage.