How This Helps
Yoga brings inner peace
Yoga is useful in the treatment of breast cancer, as it helps balance the mind, body, and spirit, increasing immune function and healing energy. Yoga can help to boost positive mindset and inner peace, which are very needed in the process of cancer treatment.
Chronic inflammation may fuel declines in physical function leading to frailty or even disability. As research studies indicate, Yoga as a complementary therapy, tends to dampen or restrict both fatigue and inflammation, and thus regular practice of yoga asanas could have substantial health benefits. 
See: Yoga Helps You & Your Baby For Gestational Diabetes
Yoga benefits for breast cancer patients
Research in breast cancer patients has shown that yoga may be able to help:
• improve physical functioning
• reduce fatigue
• reduce stress
• improve sleep
• improve quality of life
See: Yoga Mudras Types and Benefits
Gentle yoga for cancer survivors
The yoga that breast cancer patients have the ability to do might not be what you would see in a normal asana class. What’s most appropriate is a gentle approach that combines modified poses with meditation and Pranayama (breathing techniques). Sometimes women are fortunate enough to get a course created especially for people with cancer. Or they might learn of a class taught by someone who specializes in yoga therapy. Whatever the setting, the most important thing for patients is to feel comfortable and to go at their own pace.
Nadhi Shodhana: Sit comfortably and close your eyes. Lift your right hand to place your pointer and middle finger on your third eye between the eyebrows. Use your right thumb to plug the right nostril and inhale through the left nostril. At the top of your inhale, use the right ring finger & pinky to plug the left nostril and exhale out the right nostril. Inhale on the right side, plug the right nostril and exhale left. Inhale on the left side, plug the left nostril and exhale right. Continue breathing in this way, switching nostrils each time you exhale. Repeat for 7 to 10 full rounds (left side to left side) as needed, especially after chemotherapy or radiation.
Hands on heart exercise: Sit or lie down comfortably. Place both hands over your heart or over your affected breast or scar. Close your eyes and begin breathing deeply. Sense the connection between the hands and the heart. Imagine breathing light into the heart space. Sense that the light from the heart flows into the arms and hands. This light energy then re-enters your body where your palms are placed. Feel and envision this light energy flowing from the heart to the hands and back to the heart or breast. Breathe deeply and send yourself the utmost love and compassion. Feel this healing energy course through you. Practice this for 10 minutes every day.
If you get dizzy when practicing nadhi shodhana or feel ill, then wait until your nose is more clear or until a few days after treatment.
In women who have had lymph nodes removed, a number of the more strenuous yoga classes and poses may pose a risk for lymphedema. A yoga teacher who has experience with breast cancer sufferers will know that yoga classes and poses are suitable
In women with breast cancer that has metastasized to the bone, some kinds of yoga may carry a risk of fractures. In case you have bone metastasis, ask your doctor whether yoga is ideal for you, or if there is a gentle form of yoga therapy such as meditation or guided imagery. Always check with your physician before starting a yoga practice.
Science and Research
Yoga studies for cancer care
Clinical studies have demonstrated that yoga is extremely helpful in improving quality of life and physiological changes related to radiotherapy in women being treated for breast cancer. 
In studies of women with breast cancer, yoga has been shown to decrease fatigue and enhance quality of sleep, physical energy, and general quality of life.
1) In 2006, results of a yoga Study were reported by an M.D. Anderson Cancer Center study. The analysis followed 61 women getting 6 months of radiation therapy for breast cancer. Half the women took a yoga class twice a week; the other half didn’t. Compared with women who didn’t take yoga, the women in the yoga group reported having more energy and less daytime sleepiness, better physical functioning, and improved overall quality of life.
2) Researchers at Duke University published a study in 2007 demonstrating that an eight-week yoga program focusing on gentle postures, meditation, and breathing considerably lessened pain and fatigue in women who were severely ill with metastatic breast cancer. Other research shows that yoga can ease the nausea, depression, and anxiety that often accompany therapy. 
3) In another study, results were reported by a yoga study involving 126 women recently diagnosed with Stage I or II breast cancer. The women were about to receive chemotherapy or hormonal therapy. A few of the women were delegated to yoga classes over a 3-month period. The girls taking yoga had a 12% increase in fatigue, physical functioning, and quality of life compared with those from the program who didn’t take the yoga classes. 
1. Kiecolt-Glaser JK, Bennett JM, Andridge R, et al. Yoga’s impact on inflammation, mood, and fatigue in breast cancer survivors: a randomized controlled trial. J Clin Oncol. 2014;32(10):1040–1049. doi:10.1200/JCO.2013.51.8860
2. Kavita D. Chandwani, George Perkins, Hongasandra Ramarao Nagendra, Nelamangala V. Raghuram, Amy Spelman, Raghuram Nagarathna, Kayla Johnson, Adoneca Fortier, Banu Arun, Qi Wei, Clemens Kirschbaum, Robin Haddad, G. Stephen Morris, Janet Scheetz, Alejandro Chaoul, and Lorenzo Cohen, Randomized, Controlled Trial of Yoga in Women With Breast Cancer Undergoing Radiotherapy,
Journal of Clinical Oncology 2014 32:10, 1058-1065
3. Carson JW1, Carson KM, Porter LS, Keefe FJ, Shaw H, Miller JM. J Pain Symptom Manage. 2007 Mar;33(3):331-41.
Yoga for women with metastatic breast cancer: results from a pilot study.
4. Nita S. Nair, Nishu Singh Goel, Rohini W Hawaldar, Shabina Siddique, Vani Parmar, Aarti Pandey, and Rajendra A. Badwe, Journal of Clinical Oncology 2017 35:15_suppl, 527-527 , Yoga in women undergoing treatment for breast cancer: Impact on quality of life in a randomized controlled trial.