The Margie Petersen Breast Center, a Center of Excellence

The Margie Petersen Breast Center at Providence Saint John’s Health Center offers the most compassionate and innovative care in Southern California. We care for and treat the whole person: mind, body, and spirit, providing an array of services to support your emotional and physical wellbeing. Our unique partnership with the Saint John’s Cancer Institute offers an environment that combines clinical excellence with novel research, ensuring that the care you receive is outcomes-based and optimized specifically to you.

Breast Team Doctors - Margie Petersen Breast Center Breast Team Imaging - Margie Petersen Breast Center Breast Team and Caregivers - Margie Petersen Breast Center Breast Team Epigenetics - Margie Petersen Breast Center Breast Team Grumley and Patient - Margie Petersen Breast Center Breast Team Nurse Navigators - Margie Petersen Breast Center Saint John's Health Center - Breast Cancer Awareness - Margie Petersen Breast Center Breast Team Caregivers - Margie Petersen Breast Center

Clinical Excellence and Improved Quality of Life

Our care team understands that each case is unique, while we treat every patient with dignity and compassion. We understand the challenges of coping with cancer and other life-changing decisions, and we are ready to guide you every step of the way. With an outcomes-based approach and our multi-disciplinary team, we work to develop the most optimal treatment plan for you based on your needs and the input of many of our oncologists, pathologists, and scientists. clinical excellence is our commitment to you.

The Margie Petersen Breast Center provides expedited breast evaluation in a welcoming, family environment.

“I got an assessment the same day and didn’t even need a referral. I am so relieved and thankful you are here. Truly an amazing team.” -L.R.

“Thank you Dr. Grumley for your extraordinary care. My husband and I are extremely grateful for both the technical side and very personal, human side of our relationship.” -Kristy

“Dr. Parvin Peddi, MD has a glowing personality and is the true definition of the best of the best…” -Ching

Our History and Approach Patient Care

Breast Care Team - Margie Petersen Breast Center
The Breast Care Team of the Margie Petersen Breast Center is ready support you.

For almost 30 years, Saint John’s Cancer Institute has maintained a multi-disciplinary breast center dedicated to the treatment and research of breast cancer. Extraordinary supporters, such as Joyce Eisenberg Keefer and Margie Petersen, have enabled the center to become what it is today—a premiere provider that is fundamentally changing breast health.

With highly advanced diagnostic capability on-site, we can immediately identify and treat a variety of breast conditions, often seeing patients the same day and without requiring a referral. Our integrated approach to your care, which involves many specialists, including experts in surgery, medical oncology, and radiotherapy, we surrounded each patient with a dedicated team of healthcare and wellness professionals whose mission is to focus on the whole person.

Your Multi-disciplinary Team at Margie Petersen Breast Center

We are making a difference and we prove it every day.

Under the leadership of Dr. Janie Grumley, Director of the Comprehensive Breast Program at Margie Petersen Breast Center, we have successfully treated thousands of patients and look forward to providing you and your family additional information and support.

Breast Treatment & Services

Viewing breast CT scans in radiology
Our multidisciplinary team, including radiation oncology, medical oncology, and surgery, view and discuss CT scans together with radiology.

Women come to the Margie Petersen Breast Center because we can fully evaluate any breast condition in one day. By bringing several experts from other specialties together to discuss each case, we provide a more thorough assessment in less time. This process involves radiation, medical, and surgical experts, working together with radiology and other clinical staff.

Most lumps found in the breast are not cancer. If a biopsy is needed, we perform the biopsy the same day, or as soon as possible. Our team of breast specialists can quickly determine next steps and guide you through the entire process. With an annual exam, we conduct regular screenings, which is essential for early cancer detection. Patients are provided information regarding treatments, reconstruction, and supportive services during their visit.

Breast Health

Breast Health involves assessment of symptoms, conditions, and genetics, as well as prevention. (See Breast Health)

  • Genetic testing and family history are considered to determine risk and recurrence.
  • Common conditions may involve breast pain, masses (or lumps), skin conditions, and lesions.
  • Prevention involves wellness recommendations and steps you can take to be well.

Breast Evaluation

Breast Evaluation involves how we assess the extent of conditions. (See Breast Evaluation)

  • Breast exams help to establish regular assessment and early cancer detection.
  • Advanced technologies, including ultrasound, mammograms, CT scans, and Magnetic Resonance Imaging (MRI), provide visual references and measurements for the care team.
  • Biopsies aim to validate if a cancerous condition is present using scientific analysis.

Breast Cancer Treatment

Treating breast cancer may require one or more types of treatment, which are prescribed as appropriate to maximize curative effect and improve quality of life. For example, surgery may be followed by radiotherapy and chemotherapy, whereas a small, solid tumor may be treated with just radiotherapy depending on its location and the presence of metastasis. Additional treatment may include endocrine therapy (hormone therapy) and immunotherapy, which helps the immune system fight cancer. Our goal is to determine the best possible care path for you based on the type of breast cancer you have, its stage, your overall health status, and your treatment preferences. We are here to support you every step of the way.

oncolplastic surgery examples
Oncoplastic surgery is available at the Margie Petersen Breast Center at Saint John’s.


Removal of the cancerous gland, organ, or affected tissues (See Surgical Treatments for Breast Cancer)

  • May be performed with the aid of robotics
  • Used to repair tissues affected by cancer and surgery, including breast reconstruction
  • May involve oncoplastic techniques, providing immediate breast symmetry
  • Can be delivered with other types of treatment


Focused beams of energy that disrupt tumor growth (See Radiation Therapy Treatments)

  • Used primarily for solid tumors and those in difficult to reach areas
  • May require specialized imaging to determine the exact location of the tumor
  • Can be delivered externally via particle beams or internally using specialized instruments
  • Can be utilized with other types of treatment

Medical Treatment

Medication and treatments that address cancers that have or can spread to other areas (See Medical Treatments)

  • Reduces the speed of fast-growing cancer cells throughout the body
  • Encompasses systemic therapies, such as chemotherapy, biologic, endocrine, and immunotherapy treatment
  • Can be utilized with other types of treatment

Breast Reconstruction

Redeveloping the appearance of the breast after complete breast removal (mastectomy) (See Breast Reconstruction)

  • Common for women who undergo breast mastectomy
  • May take place at the time of the cancer operation or as a separate procedure
  • Encompasses different kinds of reconstruction, including direct-to-implant, autologous tissue, and nipple-areola reconstruction

The Breast Oncology team at the Margie Petersen Breast Center is ready to support you and your family. We welcome your questions and recommend coming in for an exam as soon as possible. We will discuss common conditions, treatment options, and offer additional information for each of our services as well as other cancer support services.

Contact us today.

Doctors and Nurses - Margie Peterson Breast Center
The Breast Team at the Margie Petersen Breast Center

Let’s start by answering your questions

Speak to someone today and get answers to your specific questions.

Call 310-582-7100.

Our care team is available to answer your questions. We can perform an assessment the same day, giving you confidence and options for treatment. Know that you are always well-supported and treated with compassion at the Margie Petersen Breast Center at Saint John’s.

Saint John’s Cancer Institute is leading with innovation

An Outcomes-based Approach

Saint Johns Cancer Institute Epigenetics Breast Research
Research at the Saint John’s Cancer Institute is improving patient outcomes.

The doctors at the Margie Petersen Breast Center have the advantage of working alongside other researchers including geneticists, biologists, immunologists, drug discovery scientists, and clinical trials experts at the Saint John’s Cancer Institute who collaborate with dozens of academic and industry organizations worldwide.

Together, we apply decades of research and data from thousands of cancer cases to improve our clinical practice and the quality of life for our patients. For example, we can identify biomarkers and genetic profiles that indicate who is more likely to have a recurrence of cancer, which can guide early treatment strategies and other preventive measures. As a patient, you can be assured that highly recognized doctors and peer-reviewed, published physicians and scientists are all working together to develop the best care approach and medical solutions.

Advancements in Radiotherapy

Intraoperative Radiation Therapy (IORT)

Intraoperative Radiation Therapy (IORT)
IORT delivers a targeted dose of radiation to the cancerous area at the time of surgery.

Highly targeted radiation therapy delivery that limits the radiation to just the treatment area (See Radiation Therapy Treatments).

  • Delivered during breast conserving surgery
  • Used in early-stage breast cancer
  • Treats the area that the tumor previously occupied
  • Delivers treatment in a single dose of radiation
  • Patients receiving IORT after surgery may not need future radiation
  • Reduces the need for additional care visits compared to external beam treatment
  • Lowers the risk of cancer recurrence

Accelerated Partial Breast Irradiation (APBI)

Provides the radiation oncologist greater options by focusing radiation to just a portion of the breast (See Radiation Therapy Treatments).

  • Treats a rim of normal breast tissue surrounding the surgical cavity rather than the whole breast
  • Equivalent to a five-week course of whole breast radiotherapy
  • Treatment is commonly completed in one week
  • Uses Intensity Modulated Radiotherapy(IMRT) external beam radiation therapy or High Dose Rate (HDR) brachytherapy internal catheters/balloons
  • An outpatient procedure

Programs Expansion

Saint John’s Cancer Institute Translational Immunology Program

Cancer Cell and T-cell - Immunology and Breast Research
Immunotherapies are designed to support the immune system, reducing the spread of cancer cells.

Launched in 2021, our Immunology program works to define and isolate the mechanisms by which cancer cells evade the immune system (See Translational Cancer Immunology).

The goals of the Immunology program include:

  • Identify the inhibitors of immune response that prevent the body from healing itself
  • Promote novel immuno-therapeutic agents for improving immune response
  • Develop targeted immunotherapies specific to the genetic profile of a patient
  • Predict with greater accuracy relapse-free survival

If you have questions regarding breast examination or treatment, please call today.

Dr. Janie Grumley and team of oncologists have published and co-authored dozens of peer-reviewed, breast research articles. View additional articles for Dr. Grumley at