Breast cancer is a leading cause of cancer related death in women. Triple negative breast cancer (TNBC) is a subtype of breast cancer based on an immunohistochemistry that lacks estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor-2 (HER2) expression. It is known to disproportionately affects younger women and women of African ancestry. TNBCs account for approximately 15-20% of all newly diagnosed breast cancer. Compared to other subtypes of breast cancer, including hormone sensitive disease, TNBC is associated with a high risk of distant metastases and is associated with a lower disease-free and overall survival. As TNBCs lack expression for ER, PR and HER-2, targeted therapies are ineffective. Immunotherapy has emerged as an important treatment strategy in TNBC. Traditionally, breast cancer has been considered a 'cold' cancer but the disease is highly heterogenous and TNBC appears to be more immunogenic (i.e. 'hot'). Compared to other forms of the disease, TNBC is associated with a higher mutational burden, tumor infiltrating lymphocytes (TILs) and PD-L1 expression. The later is associated with response to immunotherapy. Indeed, systemic immunotherapy is now approved as first line therapy for metastatic and unresectable PD-L1 positive TNBC. Systemic immunotherapy may also increase the incidence of pathologic complete response after neoadjuvant therapy in early stage TNBC. Improvement in pathologic complete response is weighed against rare but life-threatening immune related side-effects of immunotherapy, including adrenal insufficiency, pneumonitis causing respiratory arrest and multi-organ dysfunction syndrome.

Interleukin-2 is one of the first immunomodulating agents to be approved for cancer treatment, including renal cell carcinoma and melanoma. The cytokine plays an important role in the maintenance CD4+ regulatory T-cells and the differentiation of CD4+ T-cells into a variety of subsets. It also promotes CD8+ T-cell and NK cell cytotoxicity activity and modulates T-cell differentiation in response to antigen presentation. Systemically, IL-2 is limited by a short half-life and significant toxicities. The intralesional injection of IL-2 eliminates the undesirable grade II/III toxicities and often severe side effects of the therapy, while achieving high doses of IL-2 at the tumor site. The most common side effect of intralesional IL-2 is inflammation at the site of injection and mild flu like symptoms, including fatigue and nausea. Rarely patients may experience low-grade fever or headache, which are easily controlled by over-the-counter medications. A number of studies have reported on the use of intralesional IL-2 in management of in-transit melanoma. In this patient population, intralesional IL-2 produces a durable complete response. Much less has been published on its use in other cancers, such as breast cancer. However, there is case report level evidence to suggest that intralesional IL-2 can produce a pathologic complete response in metastatic / unresectable TNBC.

The present study considers the significant scope that remains to improve the outcomes for women with TNBC. This study seeks to build upon the growing body of evidence in support of immunomodulation in the treatment of TNBC, while also exploring a different and less toxic route of administration (i.e. intralesional as opposed to systemic). In the window of opportunity between the time of initial surgical consultation and planned OR for patients proceeding with upfront surgery, this study proposes to provide intralesional IL-2 with immediate pathologic assessment.

This 'window of opportunity' design will provide us opportunity to conduct a pilot study to evaluate the efficacy of an intralesional immunotherapy (e.g. IL-2) in early stage TNBC as a well-tolerated, low-risk intervention with the potential to improve outcomes without the toxicity of systemic treatment. As systemic immunotherapy moves from the metastatic setting to the adjuvant setting and is increasingly being used in earlier and earlier stage disease, the rationale for systemic therapy with systemic side effects to treat a local disease becomes harder to justify. This study seeks to challenge the notion that the only effective immunotherapy in the treatment of TNBC is systemic and perhaps a local administration can produce the immune response needed to affect significant pathologic response.