Pembrolizumab in Treating Patients With Hormone Receptor Positive, Localized Inflammatory Breast Cancer Who Are Receiving Hormone Therapy and Did Not Achieve a Pathological Complete Response to Chemotherapy

1. Is willing and able to provide written informed consent for the trial.

2. Is a female or male and \>/= 18 years of age

3. Has histological confirmation of breast carcinoma.

4. Has confirmed inflammatory breast cancer by using international consensus criteria:

* Onset: Rapid onset of breast erythema, edema and/or peau d'orange, and/or warm breast, with/without an underlying breast mass

* Duration: History of such findings no more than 6 months

* Extent: Erythema occupying at least 1/3 of whole breast

* Pathology: Pathologic confirmation of invasive carcinoma

5. Did not achieve pathological complete response (pCR) to any chemotherapy that was given with the intention to induce best response prior surgery. pCR is defined as the current American Joint Committee on Cancer (AJCC) breast cancer staging.

6. Is HER2 normal, defined as HER2 0 or 1+ by IHC and negative by FISH if performed; or HER2 is 2+ by IHC and negative by FISH; or HER2 negative by FISH if IHC is not performed.

7. Has positive ER or PR status. ER or PR \>/= 10%

8. Has a performance status of 0-1 on the ECOG Performance Scale.

9. Has adequate organ function as determined by the following laboratory values:

ANC \>/= 1,500 /mcL, Platelets \>/=100,000 /mcL, Hgb \>/= 9 g/dL, creatinine levels \< 1.5 x ULN, Total bilirubin \</= 1.5 x ULN, ALT and AST \</= 2.5 x ULN

10. Participants of reproductive potential must agree to avoid becoming pregnant or impregnating a partner, respectively, while receiving study drug and for 120 days after the last dose of study drug by complying with one of the following: (1) practice abstinence† from heterosexual activity; OR (2) use (or have their partner use) acceptable contraception during heterosexual activity.

Acceptable methods of contraception are: Single method (one of the following is acceptable): (1) intrauterine device (IUD); (2) vasectomy of a female participant's male partner; (3) contraceptive rod implanted into the skin. Combination method (requires use of two of the following): (1) diaphragm with spermicide (cannot be used in conjunction with cervical cap/spermicide); (2) cervical cap with spermicide (nulliparous women only); (3) contraceptive sponge (nulliparous women only); (4) male condom or female condom (cannot be used together); (5) hormonal contraceptive: oral contraceptive pill (estrogen/progestin pill or progestin-only pill), contraceptive skin patch, vaginal contraceptive ring, or subcutaneous contraceptive injection.

Female participants will be considered of non-reproductive potential if they are either:

(1) postmenopausal (defined as at least 12 months with no menses without an alternative medical cause; in women \< 45 years of age a high follicle stimulating hormone (FSH) level in the postmenopausal range may be used to confirm a post-menopausal state in women not using hormonal contraception or hormonal replacement therapy. In the absence of 12 months of amenorrhea, a single FSH measurement is insufficient.); OR (2) have had a hysterectomy and/or bilateral oophorectomy, bilateral salpingectomy or bilateral tubal ligation/occlusion, at least 6 weeks prior to screening; OR (3) has a congenital or acquired condition that prevents childbearing.

Male participants will be considered to be of non-reproductive potential if they have azoospermia (whether due to having had a vasectomy or due to an underlying medical condition).

11\. Has negative serum or urine pregnancy test for subjects of childbearing potential within 10 days before first dose.

12\. Have completed radiation (if candidate for post-mastectomy radiation) or plans to begin radiation and endocrine therapy within 28 days.

13\. If the participant has already started hormonal blockade therapy after radiation as adjuvant therapy, the patient is eligible as long as the hormonal therapy was initiated no more than 6 months before the screening day and the participant can start the study drug within 4 weeks since the completion of screening.

What this study is about