Abstract PO5-20-07: A Case of Metastatic Breast Cancer to Soft Tissue of the Thigh

Abstract Breast cancer is the most diagnosed cancer in women worldwide. The predominant cause of breast cancer mortality is metastatic disease with bone, lung, liver and brain being most common sites of metastasis. After melanoma, breast cancer is the most common cancer to have cutaneous metastatic disease and this presentation represents half of all cutaneous metastases. We are presenting a case of a 70-year-old female with distant recurrence of breast cancer to the left thigh. A 70-year-old female presented to clinic with a palpable left breast mass noted July 2022. Her medical history was notable for right sided upper lobe stage IIIB squamous cell lung cancer diagnosed in 2013 treated with chemotherapy and chest radiation (RT), menopause at 25 years old following TAH/BSO for fibroids. Family history included prostate cancer and genetic testing was negative for pathogenic mutation. Diagnostic mammogram showed a lesion in the left breast at 9:00 of 1.4 cm x 1.2 cm x1.4 cm, and biopsy showed grade 3 triple negative invasive ductal carcinoma (IDC). Her nodes were clinically and radiologically negative. She opted for breast conservation. In September of 2020 the patient had a left lumpectomy with sentinel lymph node biopsy. Final pathology (path) was pT1cN0 with two foci of IDC, grade 3, measuring 1.9 × 1.9 × 1.1 cm and 0.4 × 0.2 × 0.2 cm with negative margins. Two sentinel lymph nodes were negative for carcinoma. She received 4 cycles of doxorubicin and cyclophosphamide and started paclitaxel, but only completed 5/12 planned cycles. During these treatment cycles she was admitted twice for shortness of breath and found to have an exudative pleural effusion, repeat cytology was negative for malignancy at which point fluid did not recur. There was no CT evidence of lung nodules or plural thickening. Echocardiogram showed normal ejection fraction of 45%. PET scan was negative. Chemotherapy was stopped in February of 2021. Initial pre-operative discussion with radiation oncology indicated no contraindication to adjuvant RT. However, after simulation, it was deemed by radiation oncology that the patient was no longer a candidate for RT as during her lung cancer treatment, she had received RT of 69.4 Gy including the area of the current lumpectomy cavity. She then opted for bilateral mastectomy with immediate reconstruction in June 2021. Final path from both breasts showed no carcinoma. In November of 2021 she was admitted for shortness of breath and on CT scan was noted to have a left sided lung nodule. The patient declined biopsy and underwent a left wedge resection in January of 2022. Final path showed a 2.2. cm carcinoma consistent with breast primary that was ER 0, PR 0, and Her 2 neu 1+. She was started on capecitabine with plan for 6 months of treatment but stopped taking this after one month due to severe pain in her hands and feet. In November 2022 the patient noted a left thigh mass. Exam showed a firm, palpable thigh mass without overlying skin changes and core needle biopsy showed adenocarcinoma, favoring breast primary, ER 0, PR 0, HER 2 neu 2+ and FISH negative. PET scan showed no uptake in the chest abdomen or pelvis, however a 2.6 × 2.3 × 3.1 cm round mass in the left thigh was seen with SUV max of 8.6. She was started on traztuzumab-deruxtecan by medical oncology in December of 2022. The thigh tumor shrank significantly, however, patient discontinued after two infusions, citing intolerable hand weakness. She then received RT to the thigh. She was treated using 3D technique and 6 MV photons for a total dose of 5400 cGY, from February to March of 2023. Repeat PET June 2023 showed no avid uptake in the thigh. She has declined any additional systemic therapy. Soft tissue metastasis in distant recurrent breast cancer is uncommon and little guidance exists on clinical management. In cases of metastatic disease to the skin, hormone positive lesions can be managed with hormonal therapy. Early detection and biopsy for receptor studies may help guide therapy in cases of distant soft tissue recurrence. Citation Format: Rangel Melissa, Julia Alexieva, Alison Coogan, Lily Hussein, Elizabeth Marcus, Julie Wecsler. A Case of Metastatic Breast Cancer to Soft Tissue of the Thigh abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-20-07.