Because breast tumors of all stripes have a propensity to continually recur over several years, a study of the duration of treatment (MA.17R trial) of breast tumors containing (Estrogen and or Progesterone Receptors) was undertaken. Usual hormone therapy for breast cancer includes one or two of the following drugs (anti-estrogen drugs such as Tamoxifen, Toremifene (Fareston) and Faslodex (Fulvestrant) or an aromatase inhibitor such as Femara (Letrozole, non-streoidal inhibitor), Arimidex (Anastrozole, non-steroidal inhibitor) or Aromasin (Exemestane, a steroidal inhibitor) as adjuvant therapy. These medications are given to prevent distant tumor spread and or a new tumor of the other breast (contralateral breast). These medications were generally administered for 5 years. However, the MA.17R trial results proved that patients will experience added benefit in terms of decreased recurrence rate of the original tumor (metastases) and decreased incidence of the other breast from developing a new, second tumor if therapy is extended for 10-years. Data from the MA.17R trial (which used Letrozole (Femara) as adjuvant therapy revealed a significant and important difference in the annual incidence rate of contralateral breast cancer (other breast) 0.21% in the Letrozole treated group and 0.49% in the placebo group (P = 0.007), with a hazard ratio of 0.42. See the following Figure 2.
The above table reveals the differences in tumor recurrence between those extending taking Letrozole for extended periods longer than 5-years vs. the placebo group that stopped Letrozole therapy at 5-years (the initially recommended duration of therapy). N Engl J Med 2016;375:209-19. DOI: 10.1056/NEJMoa1604700
This trial comes on the heels of the ATLAS extended Tamoxifen trial (10-years vs. 5-years) of adjuvant therapy revealing the superiority of extending therapy with Tamoxifen for 10 years. Below Figure 3. Lancet 2013; 381: 805--16 Published Online December 5, 2012 http://dx.doi.org/10.1016/ S0140-6736(12)61963-1
Who is at high risk of recurrence after stopping only 5-years of endocrine therapy? See below:
Glenn Tisman, MD.