Breast cancer (BC) is the most frequent cancer among females that can be a leading problem of death through middle-aged females [1]. Palbociclib as an oral inhibitor of cyclin-dependent kinases 4 and 6 (CDK 4/6) present a critical function in cell cycle regulation [2] . Nowadays, this drug has been approved for the treatment of mBC of hormone receptor (HR)-positive/human epidermal growth factor receptor 2 (HER2)-negative [3]. Data show that Palbociclib is increased the response rate and duration in postmenopausal females with locally advanced or metastatic estrogen receptor (ER)-positive/HER2-negative BC [4]. This case showed the efficacy of Palbociclib as a new oral drug in mBC.

A 40-year-old female with stage 2 right BC referred to oncology clinic after modified radical mastectomy and axillary lymphadenectomy on March 16, 2014. In the history of the patient, hyperlipidemia, urinary tract infection, fatty liver grade 2 and ovarian cyst reported. She was treated with Epirubicin plus Paclitaxel for six cycles. After this treatment, the patient had the complaint of pain foot. Whole body scan showed bone metastases and the new pathology report was compatible with invasive and in situ (40%) or mixed mucinous ductal carcinoma of mBC. In immunohistochemistry staining for the tumor showed ER (Positive 1+), progesterone receptor (Positive 2+), Her2 (negative), Ki-67 (40% positive in tumoral cells), and P53 (Positive). She got 25 sessions of radiotherapy during 8 months and then was treated with Tamoxifen. Unfortunately, she went to worse condition with complaints of dyspnea. Chest computed tomography scan showed left lung metastasis in May 14, 2016 ( Figure 1 ).

She was treated with Paclitaxel plus Carboplatin for eight courses. On November 15, 2016, due to hormone receptor-positivity/Her2-negative, she was treated with Palbociclib 125 mg (per one day for two-week and one-week intervals) with Letrozole. Before treatment of Palbociclib, Platelet, WBC, and hemoglobin (Hb) were the normal that after one course of this new treatment, WBC, Hb, and platelet became 3300, 11.5, and 57000, respectively, but they returned to normal range again in other courses. In the new assessment and after 8 months of this oral combination therapy, the chest x-ray of lung showed the complete response (clearing metastasis) ( Figure 2 ). She is alive On March 1, 2018.

CDK: cyclin-dependent kinases; ER: estrogen receptor; Hb: hemoglobin; HER2: human epidermal growth factor receptor 2; HR: hormone receptor; mBC: metastatic breast cancer; Rb: retinoblastoma protein

Not to be applied.

The authors declare that they have no conflicts of interest.

None.

Mehrdad Payandeh & Edris Sadeghi: Literature search, Clinical studies, Data acquisition, Data analysis; Edris Sadeghi: Manuscript preparation, Manuscript review, Guarantor; Masoud Sadeghi: Concepts, Design, Definition of intellectual content, Literature search, Manuscript editing. Mehrnoush Aeinfar & Saba Yari: Manuscript editing.