Introduction/Background In Argentina, 18.000 new cases of breast cancer are diagnosed each year and it is the commonest cause of cancer death in women reaching 5600 deaths per year.

About 70% of all breast cancers are estrogen receptor-(ER) positive.

In postmenopausal women with advanced or metastatic, ER-positive, Her2-negative breast cancer the combination of Palbociclib (P) + Letrozol (L) or Fulvestrant (F) is a good option of treatment.

The objetive was to assess clinical benefit, evolution and safety with P associated with L or F in the context of daily practice.

Methodology We performed an observational, descriptive and retrospective study.

All patients who started treatment with P in combination with L or F between April 2016 and August 2019 were included.

Results We included 48 patients (pts), with median age 62 years (r37–85). 10 premenopausal women.

26 pts (54%) performed P + L and 22 pts (46%) P + F.

5 pts (10%) had metastatic onset. 22 pts (46%) visceral disease and 21 pts (44%) exclusive bone disease.

Clinical benefit: 8 pts (17%) stable disease, 16 pts (34%) partial response and 3 pts (6,25%) complete response.

In 23 pts (48%) an extension of 7 to 14 days of rest between cycle and cycle was necessary. Dose reduction in 12,5% (6 pts).

The most frequent toxicity were neutropenia in 25 pts (52%), G3: 60%, G2: 40%, asthenia (33,3%) and fatigue (23%). No cases of febrile neutropenia were reported.

Only 2 pts discontinued P because of adverse events.

26 pts (54%) still under treatment.

Conclusion In our experience, the response rates observed were similar with reported data. Despite the high incidence of hematological toxicity (52% neutropenia), adherence to treatment with acceptable toxicity profile was maintained.

A clinical benefit was observed in 57% of our pts with an adequate tolerance.

Disclosure Nothing to disclose