Ductal carcinoma in situ (DCIS) is breast cancer, which does not leave the milk duct and cannot spread to other parts of the body (metastasize). Before the mid1980s, it was usually discovered by finding a breast lump. But since that time, it is more commonly diagnosed by mammography. The usual finding is a clustered group of calcifications, as noted in the image above. Yet even mammography has improved dramatically, diagnosing DCIS at a steadily decreasing size.
Furthermore, needle biopsy technology has allowed the removal of increasingly large samples of tissue. Currently, approximately 20% of newly diagnosed DCIS is considered extremely small and, in many cases, has been entirely removed by the needle biopsy, with no further tumor discovered at the time of lumpectomy. DCIS completely removed by needle biopsy is called minimal-volume DCIS (mDCIS).
Breast physicians, including surgeons, oncologists, and radiation oncologists, have begun to question the need for radiation and or hormonal therapy for mDCIS. A recent study from Memorial Sloan-Kettering Cancer Center serves as evidence-based guidance in the care of this problem. All the patients in this study were diagnosed with DCIS by core needle biopsy. Furthermore, they underwent a lumpectomy, at which time no further cancer was detected. There were 290 cases studied in which approximately 72% did not receive radiation. The average follow-up time was about seven years though many patients were followed for over ten years.
Within the entire group of patients with mDCIS, approximately 4% had a recurrence at five years and 12% at ten years. Most importantly, those patients with radiation therapy following lumpectomy have a 10-year recurrence rate of only 6.5% compared to 14% for those not receiving radiation. Only a small group of 19 women received both radiation and hormonal therapy. None experienced a recurrence in the affected breast.
We have been aware that women who develop breast cancer in one breast have a modest increase in the incidence of cancer in the opposite breast (about 0.5% per year). When examining the entire group of women, the risk of a recurrence in the affected breast was higher than the risk of cancer developing in the opposite breast. However, among those receiving radiation, recurrence rates were less frequent than new cancers in the opposite breast. Endocrine therapy also was noted to reduce the risk of cancer in both the affected and unaffected breasts.
Entering this study, the researchers hypothesized that patients with mDCIS who underwent breast-conserving surgery with no additional therapy would have a very low risk of recurrence. If true, they expected that the risk of recurrence or new cancers in the affected breast and the opposite breast would be similar. This study did not support their hypothesis. They noted a significant increase in recurrence in the affected breast in this group of patients. They also noted that even though these were patients with tiny cancers, there was a significant benefit from both radiation and hormonal therapy. This study suggests that any size of DCIS in the breast should be considered clinically relevant and treated accordingly.