Trial of Exemestane +/- MM-121 in Postmenopausal Women With Locally Advanced or Metastatic Estrogen Receptor Positive and/or Progesterone Receptor Positive Her2 Negative Breast Cancer

The study is a double-blind, randomized Phase 2 trial of Exemestane +/- MM-121. The trial is
designed to demonstrate whether MM-121 + Exemestane is more effective than Exemestane alone
in ER+ and/or PR+ and Her2 negative breast cancer patients that have failed first-line
anti-estrogen therapy in the locally advanced or metastatic setting and patients that have
progressed during (or within 6 months of completing) adjuvant treatment with a non-steroidal
aromatase inhibitor (AI)and/or tamoxifen. Patients will be treated until radiologic or
clinical progression of their disease is documented. Local radiologist and/or PI assessment
is accepted.

Inclusion Criteria:

- Locally advanced or metastatic breast cancer

- Histologically or cytologically confirmed ER+ and/or PgR+ and Her2 negative breast
cancer

- ≥ 18 years of age

Exclusion Criteria:

- Received prior treatment with exemestane

- Extensive visceral disease (rapidly progressive, life-threatening metastases,
including symptomatic lymphangitic metastases)

- Symptomatic CNS disease