The overall purpose of this study is to investigate whether younger subjects report pain with pegfilgrastim (or biosimilar substitution) more often and/or at higher levels (greater intensity) than older subjects.This study will be carried out throughout the course of your chemotherapy treatment, which will be prescribed by your study doctor. Participation in this study will not affect your cancer treatment.

This study will measure pain using ESAS self-reported pain scores over the course of one week following each dose of pegfilgrastim (or biosimilar substitution). At the end of that week, blood will be drawn from each subject to directly measure the WBC/ANC, which can then be compared to self-reported pain and evaluated for any correlation. Finally, subjects will be divided into two groups by age: 45 years or younger, and over 45 to look for any differences in pain or WBC/ANC measurements based on age.

Inclusion Criteria

Subject must meet all the following applicable inclusion criteria to participate in this study:

1. Written informed consent and HIPAA authorization for release of personal health information. NOTE: HIPAA authorization may be included in the informed consent or obtained separately.
2. Age ≥ 18 years at the time of consent
3. Female
4. Histological or cytological confirmation of invasive breast cancer.
5. Planned to undergo adjuvant or neoadjuvant chemotherapy treatment for invasive breast cancer AND pegfilgrastim (or biosimilar substitution) treatment for neutropenic prophylaxis.
6. Ability to read and understand the English and/or Spanish language
7. As determined by the enrolling physician, ability of the subject to understand and comply with study procedures for the entire length of the study

Exclusion Criteria

Subjects meeting any of the criteria below may not participate in the study:

1. Uncontrolled intercurrent illness/medical condition or psychiatric illness/social situations that would limit compliance with study requirements as determined by the investigator
2. Have previously received chemotherapy or radiation other than the first cycle of the planned adjuvant or neoadjuvant chemotherapy as indicated in Inclusion #5
3. Taking chronic narcotics, as determined by treating physician
4. Diagnosis of distant metastatic breast cancer
5. Diagnosis of a chronic pain syndrome (e.g. fibromyalgia, severe osteoarthritis, etc.)
6. A baseline ESAS pain score of greater than 8.

Female patients undergoing neoadjuvant or adjuvant chemotherapy for breast cancer who will receive pegfilgrastim (or biosimilar substitution) during their treatment.