The patient is an 80 year old male with a past medical history of atrial fibrillation with sinus block with dual chamber pacemaker placed in November 2006, and a complicated oncologic history including breast cancer in the 1970s treated with left-sided mastectomy and axillary lymph node dissection; prostate cancer treated with intensity modulated radiation therapy (IMRT) in 2001; mucosal melanoma with metastases to small bowel treated with small bowel resection in 2005; and multiple skin cancers. He was treated with a total thyroidectomy for anaplastic thyroid carcinoma in March 2008, followed by post-operative cisplatin-based chemo-radiation therapy to the surgical bed and the draining lymph nodes. A subsequent left lung nodule was treated with thoracotomy and wedge resection in December 2008, with documented metastatic anaplastic thyroid carcinoma on pathology. He also received one cycle of Abraxane and Bevacizumab in February 2009.
The patient had been asymptomatic and in his usual state of health until July 2009 when he presented with a 2 month history of decreased exercise tolerance and orthostatic hypotension. Workup revealed a loss of atrial function, leaving the patient dependent on his pacemaker. An outpatient echocardiogram was concerning for "intracavitary irregular densities" in the right ventricle and right atrium. CT Chest with contrast revealed a 5.1 × 4.8 cm right atrial mass, with a broad base of attachment at the right atrial posterior wall and extension into both the inferior and superior vena cava. There was a notable displacement of pacemaker leads. The right ventricle also demonstrated an irregular lobulated 6.8 × 2.5 cm mass attached to the ventricular septum. Retrospective evaluation of a prior PET-CT from June 2009 confirmed increased FDG uptake within the right atrium and right ventricle.
In mid-July 2009, the patient was admitted to University of California San Francisco Moffitt Hospital for cardiac telemetry and management of this intracardiac mass. Admission labs showed thrombocytopenia with platelets ranging between 20 and 35. The differential diagnosis for right heart masses included metastases from anaplastic thyroid carcinoma or melanoma, a new primary cardiac malignancy, or a thrombus.
A Fibrinogen level was within normal limits, and hematology smears were negative for schistocytes. A bone marrow biopsy demonstrated a normocellular marrow for the patient's age with mixed trilineage hematopoesis and no evidence of lymphoma or thrombus. A trial of dexamethasone for suspected idiopathic thrombocytic purpura (ITP) did not impact the thrombocytopenia. The differential diagnosis for the thrombocytopenia therefore remained a consumptive coagulopathy secondary to tumor, versus tumor-associated immune thrombocytopenia.
After careful consideration at a multi-institutional tumor board, it was decided to treat these intracardiac metastases with radiation therapy. A pre-treatment electrophysiologic interrogation showed intermittent loss of capture by the pacemaker, most likely secondary to growth of the intracardiac mass. Therefore, a new pacemaker with epicardial leads was emergently placed. During this procedure, biopsy of the intracardiac mass was performed, confirming metastatic anaplastic thyroid carcinoma.
Radiation therapy to the right atrium and part of the right ventricle was initiated at 2.5 Gy per fraction for 15 fractions to a total dose of 37.5 Gy, with an intended maximum dose in the tumor areas just exceeding 40 Gy (see below) (Figure ). Paclitaxel (50 mg/m2) was administered concurrently on days 1 and 8 of radiation treatment.
Figure 1 Radiation treatment plan for patient with right atrial and ventricular metastases from anaplastic thyroid carcinoma. The PTV is delineated in red and received 37.50 Gy in 15 fractions, prescribed to the 87% isodose line. The median left ventricle (purple) (more ...)
During the course of his radiation treatment, the pacemaker demonstrated full capture. A single episode of ventricular undersensing with pacing stimuli during T-waves was successfully addressed by the reprogramming of the device. Transcutaneous pacer was available during treatment should failure of the primary pacing device occur. Echocardiograms during radiation treatment showed that the intracardiac mass had not increased in size. The patient required platelet transfusions approximately every 48 hours, and his platelet count held steadily around 18 to 20. Given his leukopenia and sepsis, Abraxane was withheld after two courses.
After discharge, the patient participated in regular activities of daily living, including work-related meetings and exercise on the treadmill, but experienced persistent dyspnea on exertion. His pacemaker continued to demonstrate full capture without evidence of dysfunction.
In late August 2009, less than one month after completion of treatment, a PET-CT showed decreased FDG uptake right atrium (maximum SUV decreased from 27.9 to 7.8) and stable FDG uptake within the right ventricle (Figure ). There was some questionable uptake in the interventricular septum, representing normal physiologic uptake or residual disease. Unfortunately, multiple pulmonary and chest wall metastases were subsequently detected.
Figure 2 PET Response to treatment of an intracardiac metastases in the R ventricle and atrium. The top panel demonstrates a PET-CT scan of the hypermetabolic tumor mass prior to treatment on June 8 2009; the lower panel shows the tumor mass with notably decreased (more ...)
The patient completed one additional course of palliative radiation therapy to a symptomatic left chest wall metastasis. He died in his home two months after completion of radiation therapy.