Sometimes a woman has a new breast cancer diagnosis. It could be DCIS [Ductal Carcinoma In Situ]. Dr. Anton Titov, MD. How to find optimal breast cancer therapy in DICS? How to make therapy decisions that are optimal for individual breast cancer patient. How to treat breast cancer according to the latest clinical trial results. What a patient with breast cancer should discuss with her oncologist? Dr. Anton Titov, MD. What potential molecular tests on the tumor could be done to optimize therapy decisions in DCIS? Dr. Jack Cuzick, PhD. It's fair to say that none of the molecular markers for breast cancer are well enough established to be used clinically. The only exception is estrogen receptor and progesterone receptor. Those receptors are important for deciding whether to consider endocrine therapy of breast cancer. It could be either tamoxifen or aromatase inhibitors (anastrozole, letrozole or exemestane). The use of HER2 tumor maker is still quite interesting. There will be important therapy decisions to be made based on HER2 tumor marker status. Dr. Jack Cuzick, PhD. But I don't think we are in a position to recommend HER2 marker testing routinely. There is a whole range of other tumor markers for breast cancer. They are important for giving us insights not only into how to treat DCIS. Tumor marker give us important information about a pathogenesis of breast cancer. Some DCIS [Ductal Carcinoma In Situ] is actually on a molecular pathway that's going to lead to invasive breast cancer. There are other DCIS tumors that will not become invasive cancers. A large proportion of women with DCIS are being over-treated now. Excessive treatment of breast cancer DCIS happens often. Because physicians fear that one of patients with DCIS is in the subset that will progress to invasive ductal carcinoma. Dr. Jack Cuzick, PhD. But at the same time excessive cancer therapy exposes people to unnecessary side effects of radiation therapy. Excessive treatment of breast cancer sometimes leads to unnecessary extensive surgery. Dr. Jack Cuzick, PhD. Absolutely correct! There is no doubt that we are treating more DCIS than we need to. The challenge is to slowly move back on treatment without endangering the safety of patient with breast cancer. I think that radiotherapy is the area where there is the biggest opportunity to reduce treatment. Because radiotherapy is given to almost every patient with breast cancer. Whether or not radiation therapy is really needed for small low-grade breast tumors is a very open question. DCIS in breast cancer is one of those cancers where P4 medicine can make a lot of success. Dr. Anton Titov, MD. Precision medicine can help a lot of patients with DCIS. Of course, you are absolutely correct.