“Ipsilateral”, as defined by the National Cancer Institute, means “on the same side of the body as another structure.” True to form, ipsilateral breast cancer is when there is a recurrence of cancer in the same breast as a previous occurrence of cancer (i.e. a new tumor in the same breast there was a former tumor in). It stands opposite to contralateral breast cancer, where a new tumor develops in the opposite breast from where there was a previous cancer. While contralateral breast cancer tends to either be an entirely new manifestation of cancer or a metastasis, ipsilateral breast cancer is more nuanced. Usually originating after a lumpecotmy, or a breast-tissue conserving surgical intervention, ipsilateral breast cancer is predominantly a recurrence of the initial cancer.
Because breast cancer recurrence is an unwanted outcome after lumpectomy, lots of research has been conducted on when, where, and how often ipsilateral breast cancer recurrence occurs. Here, we’ll walk you through a few studies examining ipsilateral breast cancer that will hopefully provide some insight into the risk factors associated with ipsilateral breast cancer, and prognoses of those who experience it.
This literature review looks at when breast conserving surgeries are usually done globally, and when, based on prior research, they should be done in order to limit post-operative complications, including ipsilateral breast cancer recurrence. Overall, the researchers find that mastectomy is done in a large number of cases, however, this may not always be necessary. Absolute deal-breakers for breast conserving surgery were noted in only about 20% of cases; these include locally widespread disease (large tumors), multiple tumors, malignant calcifications, late-stage disease, patients with mutations on BR-CA1 or other high-risk genes, and an irradiated thoracic wall (extensive inflammation). If breast-conserving surgery is done on these types of tumors, then the risk of ipsilateral breast cancer recurrence are higher than average.
Classification of ipsilateral breast tumor recurrences after breast conservation therapy can predict patient prognosis and facilitate treatment planning
When you have ipsilateral breast cancer, it can arise in one of two ways- as a completely new tumor, or recurrence of a former tumor. This study aimed to categorize ipsilateral breast cancer cases as from one of these two origins using two distinct classification methods. Overall, the researchers found that about 50% of instances were new tumors and 50% were recurrences by both
classification systems. They also found trends in contralateral breast cancer rates associated with new tumors, and that systemic metastatic disease was associated with recurrent tumors; the researchers conclude that for new cases of ipsilateral breast cancer, therapeutic interventions may be targeted towards the origin of the new tumor, whether it is new or recurrent, for more optimal outcomes.
Ipsilateral breast tumor recurrence in early stage breast cancer patients treated with breast conserving surgery and adjuvant radiation therapy
This retrospective cohort study followed a series of people being treated for stage 0-II breast cancer with a lumpectomy and adjuvant radiation, and assessed whether or not they developed ipsilateral breast cancer. They then assessed the new tumor for gene mutation concordance; that is, they checked whether or not the ipsilateral cancer had the same genetic markers as the original removed tumor. In a way, this is similar to the above study, in determining whether or not the new cancer is genetically related in any way to the original cancer. However, unlike the previous study, they found that up to
80% of surveyed cases of ipsilateral breast cancer had the same gene mutations as the original tumor; specifically estrogen and progesterone receptor mutations were significantly associated with ipsilateral breast cancer, while HER2+ cancers were not at a significantly increased risk . Interestingly, they also found that those being treated with endocrine (hormone) therapy for their primary tumor and those with larger tumors (greater than 1.5 cm) were less likely to develop ipsilateral breast cancer.
This study, similar in design to the above study, followed a cohort of women with breast cancer that were treated with lumpectomy, radiation, and adjuvant therapy. Researchers found that 9.7% of their study sample developed ipsilateral breast cancer, with 62% of cases occurring within 5 years after surgery, and 88% of cases occurring within 10 years of surgery.
They noted that risk factors included not receiving hormone therapy, specifically Tamoxifen, and being under 50 years old, although none of these risk factors were statistically significant. The researchers did find that estrogen receptor mutations were significantly associated with ipsilateral breast cancer, but found no association with progesterone receptor status, and did not appear to examine HER2 mutation status.
So, what can this tell us?
Based on current and former research, the consensus on ipsilateral breast cancer seems to be that it is overall a rare outcome following lumpectomy. Some factors that might reduce the chances of developing ipsilateral breast cancer even further include the use of endocrine therapy, such as Tamoxifen. However, undergoing lumpectomy at a younger age or having genetic markers such as estrogen receptor or progesterone receptor mutations might make it more likely that ipsilateral breast cancer occurs up to 10 years in the future.
However, that’s not to say that the presence or absence of these factors will make or break your chances of tumor recurrence. Every cancer is unique, for better or worse; the best predictor of long-term outcomes after lumpectomy will be your medical team, and yourself, as an advocate of your own care. However, we hope that these studies have helped you better understand the possible risks and benefits regarding your treatment when considering ipsilateral breast cancer as a potential long-term complication.
If you’ve had experience with ipsilateral breast cancer, and want to share your story, we’d love to hear it- let us know here. And if you’re looking for a place to meet with others facing similar difficulties in cancer treatment and recovery as you are, try joining one of our support groups here.