1738. The Imaging Appearance of Pseudoprogression in Breast Cancer Treated with Immunotherapy
Authors * Denotes Presenting Author
  1. Angela Chen *; University of California San Diego
  2. Mohammad Eghtedari; University of California San Diego
  3. Rebecca Rakow-Penner ; University of California San Diego
  4. Haydee Ojeda-Fournier; University of California San Diego
Immunotherapy has shown clinical efficacy in patients with various type of advanced tumors. For example, anti-PD-1 therapy, pembrolizumab, has shown to provide durable antitumor activity and high 5-year overall survival rates in advanced non-small cell lung cancers. Pseudoprogression, a delayed tumor size shrinkage following an increase tumor burden is commonly observed. In lung cancer, up to 5% of patients treated with pembrolizumab presented with pseudoprogression. A review of the literature has yielded no reports of pseudoprogression in breast cancer patients who received immunotherapy. As part of a clinical trial, we observed several patients with breast cancer undergoing neoadjuvant therapy with SD 101 intra-tumoral immune therapy agent with imaging appearance of progression of disease. With no breast cancer reference for pseudoprogression, it was unsettling to see what otherwise would indicate progression of disease. The purpose of this study is to document the rate of pseudoprogression in a single institution participating in a clinical trial of breast cancer immunotherapy with SD 101.

Materials and Methods:
After obtaining IRB approval, we retrospectively reviewed a single institution's experience with patients who had undergone neoadjuvant chemotherapy as part of the Investigation of Serial Studies to Predict Your Therapeutic Response with Imaging and Molecular Analysis 2 (I-SPY2). Subjects enrolled in the I-SPY2 trial that were treated with intra-tumoral injections of SD 101 (a toll-like receptor 9 (TLR9) agonist CpG-C class oligodeoxynucleotide) added to standard neoadjuvant therapy (weekly paclitaxel x 12, doxorubicin & cyclophosphamide every 2-3 weeks x 4, T/AC) from 02/2019-06/2020 were included in the analysis. Demographics, anthropometrics, MRI reports, pathology reports, laboratory results and clinical notes were reviewed.

10 patients (mean age of 47 [SD:9.9]) with 11 lesions (invasive ductal carcinoma in 8, invasive ductal and lobular carcinoma in one, and invasive lobular carcinoma in one patient) were included. 5 patients (50%) had triple negative breast cancer. 5 patients (50%) reported family history of breast cancer. 3 patients tested positive for BRCA 1 mutation and 2 for BRCA 2 mutation. 6 patients were postmenopausal. 2 patients withdrew before study completion, one due to abnormal lab value and one due to drug side effects. Average number of MRI scans reviewed per patient was 4.1 [SD: 1.1]. The average follow-up time was 115 days [SD: 41.2]. 7 patients presented with decrease in tumor sizes following immunotherapy. 3 patients with 3 lesions had increase in size on day 20, day 17, day 25 after starting the treatment regimen. The same lesions were observed to shrink in size on day 83, day 47 and day 63. The maximum size increase for each lesion was 21%, 56% and 49%.

Pseudoprogressions was observed in 30% of the patients who underwent therapy with SD 101 intra-tumoral immunetherapy. It is important for breast radiologists to recognize that psuedoprogression does not represent failure of therapy or progression of disease.