Inflammatory Breast Cancer (IBC) is the most lethal and rare form of breast cancer. It is characterized by rapid progression, local and distant metastases, younger age of onset, and lower overall survival compared with other breast cancers. Although IBC, like non-IBC breast cancers, is a heterogeneous disease and can occur as any of the five molecular breast cancer subtypes, they are most commonly either triple negative; or ER-, PR- and HER2+ overexpressed. There is no specific IBC treatment; thus, it seems feasible to find a therapeutic for this deadly disease. Our published data demonstrates that Ganoderma lucidum (Reishi) inhibits the viability of the triple negative IBC SUM149 cell line, but not of MCF10A noncancerous mammary epithelial cells. Consequently, in this study, we aimed to investigate Reishi effects in the viability of the ER-, PR-, HER2+ IBC cells lines SUM190 and KPL4. Also we studied the effects of Reishi on IBC cells when treated in complement with the HER2 Tyrosine Kinase Inhibitor, lapatinib (Tykerb®). Our hypothesis is that Reishi chemosensitizes IBC cells to lapatinib therapy. Herein, SUM190 and KPL-4 cells were treated with increasing concentrations of lapatinib and/or Reishi for 24 or 72h. Our results demonstrate that SUM190 and KPL-4 cells are sensitive to Reishi treatment. The combination of lapatinib plus Reishi reduced cell viability of SUM190 cells to 70% when treated with a concentration of 0.5mg/mL Reishi for 24h. Also, our data shows a reduction in cell viability of 94% in KPL-4 cells treated with lapatinib plus Reishi for 72h. We are currently directing our efforts to continue studying the contribution of Reishi in IBC cells when treated with lapatinib after 24 or 72h. Our results provide evidence that Reishi inhibits cancer cell viability and chemosensitizes IBC cells to lapatinib therapy, highlighting its anti-IBC-therapeutic potential. We thank Dr. Kurebayashi (Kawasaki Medical School, Japan) for providing KPL-4 cells. This project was sponsored by NIH/NCI #1F31CA174307 to ISA, Title V PPOHA US Department of Education #P031M105050 to UCC, NIH/RCMI #G12MD007583 to UCC, NIH/INBRE #5P20GM103475 to UPR/UCC and a research donation from the Commonwealth of Puerto Rico to UCC's University Center of Integral and Complementary Medicine (CUMIC)/MMM.

Citation Format: Yismeilin Feliz-Mosquea, Ivette Suárez-Arroyo, Luis A. Cubano, Michelle M. Martínez-Montemayor. Synergistic effect between Ganoderma lucidum (Reishi) and lapatinib in HER2+ inflammatory breast cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3219. doi:10.1158/1538-7445.AM2014-3219