Physicians & Staff

Zafer Yildirim, MD, PhD, ABIM

Dr. Yildirim, MD, PhD, ABIM specializes in medical oncology and hematology. He brings high quality, comprehensive cancer care to patients in the Lower Columbia Region. Dr. Yildirim is board certified by the American Board of Internal Medicine in Hematology/Oncology and Internal Medicine. His specialized training and background will serve the patients of the Lower Columbia Region well.

Dr. Yildirim has spent over 14 years completing his post-graduate studies at prestigious universities and medical schools throughout the United States:

  • PhD: 1990-1996
    Case Western Reserve University in Cleveland, Ohio
  • Internal Medicine Residency: 1996-1999
    Michigan State University College of Human Medicine/Spectrum Health in Grand Rapids, Michigan
  • Critical Care Fellowship: 1999-2000
    St. Louis University/St. John's Mercy Medical Center in St. Louis, Missouri
  • Hematology/Medical Oncology Fellowship:2000-2003
    University of Vermont/Fletcher Allen Health Care in Burlington, Vermont

According to Dr. Hyman Muss, Director of Hematology/Oncology Fletcher Allen Health Care in Burlington, Vermont, "Dr. Yildirim personifies all those qualities one desires in a hematologist/oncologist- compassion and dedication to patient care and caring, excellence, and cutting-edge knowledge."  

Prakash Thapaliya, MD

Dr. Thapaliya has multiple board certifications from the American Board of Internal Medicine, in hematology, medical oncology, and internal medicine.

Dr. Thapaliya's extensive training includes a Bachelor in Medicine and Bachelor in Surgery from Manipal College of Medical Sciences in Pokhara, Nepal. He practiced internal medicine at The Reading Hospital and Medical Center in Reading Pennsylvania where he was named Resident of the Year in 2008, and practiced hematology and medical oncology at the Mayo Clinic in Arizona. Most recently Dr. Thapaliya has served as a hematologist at Palo Verde Cancer Specialists in Glendale, Arizona.

Growing up in Nepal, the home of Mt. Everest, Dr. Thapaliya developed an affinity for hiking and mountaineering which he enjoys to this day.

Stephanie Roberts, BS, MPAS, PA-C 

Stephanie Roberts is a board certified Physician Assistant working at the Lower Columbia Regional Cancer Center.

She is originally from Ohio. She moved to the Pacific Northwest in 2004 to enjoy the lifestyle and outdoor activities of the region. 

Stephanie has worked in Oncology since becoming a PA and finds it a very rewarding field. She is also trained as a genetics educator and can work with patients regarding their cancer risk.

Education and Training:

  • College: The Ohio State University, BS, Zoology 1996
  • Medical School: University of Florida Physician Assistant program, MPAS 2001
  • Hospital Staff Appointments: St. John Medical Center, Longview

Karla Houk, RN, BSN, OCN

Karla Houk is Manager of the PeaceHealth Lower Columbia Cancer Center.  

Karla is an experienced and knowledgeable oncology nurse and has functioned in a variety of capacities as an oncology nurse in her 20-year span of nursing.  Karla grew up in eastern Washington, graduated from Pacific Lutheran University with a Bachelors of Science in Nursing degree.  She is an Oncology Certified Nurse, Chemotherapy Certified Nurse and has served as an educator for the American Cancer Society.

St. John Medical Center
1615 Delaware St
Longview, WA 98632

Medical Oncology