How does secondary breast cancer differ from primary breast cancer in younger patients?

This paper compared primary and secondary breast cancers in adolescents and young adults.

Primary breast cancer refers to the first cancer that starts growing from the breast. Secondary breast cancer refers to breast cancer on the other breast that did not occur at the same time as the inital cancer, breast cancer that has spread to distant sites in the body or a subsequent breast cancer more than 5 years after diagnosis with the first breast cancer. Breast cancer is the most common cause of cancer-related death in adolescents and young adults (those aged between 15-39 years).  Studies have found differences between younger and older patients with breast cancer. 

The authors studied the national cancer database, which has data on cancer from more than 1500 hospitals. A total of 106,771 adolescent and young adult females who had breast cancer were studied.

Patients with a secondary breast cancer tended to be older than patients with primary breast cancer. Secondary breast cancers were more frequently estrogen receptor negative (absence of estrogen receptor) and progesterone receptor negative (absence of progesterone receptor). Secondary breast cancers were more likely to have spread to other parts of the body at the time of diagnosis than primary breast cancers. Patients with a secondary breast cancer were less likely to receive adjuvant therapy (treatment given after surgery). They were more likely to undergo mastectomy (removal of entire breast).

Overall, the average overall survival was 134 months for primary breast cancer and 114 months for secondary breast cancer. After 3 years,  89% of primary breast cancer patients had survived  compared to 79% of secondary breast cancer patients. In patients with secondary breast cancer, being estrogen receptor and progesterone receptor negative were associated with decreased overall survival. 

The authors concluded that patients with a secondary breast cancer tended to have a worse outcome and research should look into ways to improve treatment. 

The authors did not have information about the causes of death, which might be different for primary and secondary breast cancers.