Hormone Positive HER2 Negative Breast Cancer Metastatic to the Rectum: A Case Report

Background: The rectum is an uncommon site for metastases from Invasive Ductal Carcinoma (IDC) of the breast, and it poses risks such as perforation and obstruction. Case Report: A 50-year-old non-diabetic, non-alcoholic, and nonsmoker premenopausal female patient diagnosed with rectal metastasis primarily originating from breast cancer. In 2009, the patient was diagnosed with stage IV hormone positive, Her-2 (+2) negative, FISH positive right breast cancer with cervical (C6) vertebrae metastasis seen on PET scan. As she had oligo metastasis with a single bony focus, she was treated with intent to cure. For this purpose, she received radiation therapy to the cervical vertebrae, resulting in a complete response. This was followed by pseudo-neoadjuvant chemotherapy with six cycles of Docetaxel and trastuzumab. The patient then underwent a right-modified radical mastectomy. The pathology showed no complete response with residual 2.5 cm invasive carcinoma (PT2), and 4 out of 25 Axillary lymph nodes were positive for metastases (PN2). She was given (pseudo) adjuvant radiotherapy to the chest wall and lymphatics and was started on (pseudo) adjuvant tamoxifen. Trastuzumab was completed for one year as a (pseudo) adjuvant setting. Her disease seemed to be cleared up as no new cancer signs were reported by follow-up full body scans (CT/PET). After seven years, in May 2016, her PET-CT scan showed multiple new hypermetabolic osseous lesions, in keeping with metastasis involving the right shoulder, mid-thoracic spine, left aspect of L5, right sacrum, and the greater trochanteric region of the left femur and left ischium. She also presented a new hypermetabolic retroperitoneal paracaval lymph node, in keeping with metastasis. The new ill-defined hypodensity in the left hepatic lobe was associated with increased FDG uptake, which is suspicious for early metastasis. She also presented a tiny right lung peri-fissural nodularity that was too small to be characterized by PET. She was treated with Zoladex 3.6 mg injection monthly, Femara 2.5 mg daily, Palbociclib 125 mg PO daily for 21 days over a 28-day cycle, and Denosumab 120 mg monthly. The treatment was initiated in Singapore. As previously stated, Her-2 testing was reported as negative. The patient went into complete remission for more than six years, as documented by the PET scan conducted on January 19, 2022. Later, in June 2022, the patient developed signs and symptoms of intestinal obstruction (abdominal pain, nausea, and vomiting) and was diagnosed with rectal cancer metastases of breast origin. Conclusion:  As the patient first developed breast cancer with oligo-bony metastasis, which was successfully treated with chemotherapy and radiotherapy, but later relapsed in the lung, liver, lymph nodes, and multiple bony sites. She was treated successfully via hormonal and targeted therapy. Finally, she relapsed in the form of rectal metastasis.