Malignant phyllodes tumor of the left atrium

Abstract

Metastatic tumors to the heart usually involve right sided chambers. We report a rare case of malignant phyllodes tumor of breast with metastatic involvement of left atrium occurring through direct invasion from mediastinal micro-metastasis and presenting as a left atrial mass causing arrhythmia.

A 50-year-old lady presented to the casualty department, with history of an episode of sudden onset New York Heart Association (NYHA) class IV dyspnea and transient palpitation, occurring about 3 h prior to presentation and subsiding spontaneously. Her Electrocardiogram done in a primary hospital showed supra-ventricular tachycardia.

At presentation, she was asymptomatic, with unremarkable physical examination. There was past history of excision of right breast lump with axillary clearance for a malignant mass a year ago, followed by radiation therapy. On echocardiography, a large LA mass was seen occupying almost whole of the LA cavity, with probable attachment to a pulmonary vein (Fig. 1A). The mass had no attachment to inter atrial septum. The LA appendage was free of thrombus. The mass was intermittently protruding through the mitral orifice. Remaining echocardiographic assessment was unremarkable. In view of recent history of resection of malignant breast tumor, it was considered essential to rule out malignant nature of the LA mass and also to look for local metastases in the surrounding thoracic viscera before planning definitive treatment. Hence, probabilities of LA myxoma, breast metastasis or LA thrombus were considered and computed tomography (CT) of thorax with contrast was advised to further characterize the mass. CT scan was performed on dual source dual energy 64-slice MDCT scanner before and after injection of 75 ml non-ionic iodinated contrast. It revealed a large (55 × 39 × 41 mm) hypo dense filling defect lying along postero-lateral wall and roof of LA (Fig. 1B), extending from left superior pulmonary vein. The diagnostic possibilities of thrombus and metastatic tumor were considered. In view of absence of metastatic nodules in lung parenchyma or in mediastinum, thrombus was considered more likely, but the scan did not allow for clear differentiation between bland thrombus and tumor tissue. Similar attenuation value for thrombus and tumor on CT scan is a known pitfall during tumor evaluation.¹ In view of potential for systemic embolization and/or acute mitral valve obstruction, early surgical resection was performed. Left atriotomy revealed a large tumor mass attached to left superior pulmonary vein, occupying LA chamber and partially protruding into left ventricular inflow. Presence of patent foramen ovale was ruled out intra-operatively, since, it could be a potential explanation for the metastatic route from breast to left atrium without involving right heart, as revealed in CT scan. The mass was resected and sent for histopathological examination (Fig. 1C). The post-operative recovery was uneventful. Meanwhile, her previous pathological records were reviewed, which revealed the following. A breast tumor measuring 3.5 × 3 × 3 cm in size was resected a year ago with axillary clearance. The base of the mass and soft tissue margins were free of abnormal tissue. All the resected lymph nodes were free of tumor. On histologic examination, the breast lump had features of malignant phyllodes having components of spindle cells (Fig. 1D – 1) as well as neoplastic chondrocytes with high mitotic activity (Fig. 1D – 2). Immunohistochemical profile was negative for ER (Estrogen receptor), PR (Progesterone receptor) and Her2eu. The cardiac tumor revealed histomorphologic features of a sarcoma (Fig. 1E – 1) with features very similar to that of the spindle cell component of the breast mass (Fig. 1E – 2), indicating common origin for both the tumors.

Fig. 1.

A: Echocardiogram in parasternal long axis view showing large mass in left atrium (arrow heads); MV -mitral valve, LV- left ventricle. B: 64-slice MDCT with contrast showing filling defect in left atrium. C: Surgical specimen excised from left atrium. D: H&E stain sections of breast tumor showing features of malignant Phyllodes having components of spindle cells (D1) as well as neoplastic chondrocytes with high mitotic activity (D2) (arrows). E: H&E stain sections from left atrial mass (E1) & breast mass (E2) showing histo-morphologically similar spindle cell components indicating common origin for both neoplasms. F: PET scan showing abnormal tracer activity involving soft tissue mass occupying entire left superior pulmonary vein and partially entering adjacent atrial cavity (large arrow). Small arrow indicates focal abnormal tracer activity in the anterior wall of ascending aorta suggesting malignant embolism. G: Tomographic scan one month after atrial tumor resection revealed pulmonary nodule (arrow) gaining access into the adjacent pulmonary vein (arrow head). H: Positron emission tomography after tumor excision – the Maximum Intensity Projection image showing increased metabolic activity in left atrium, extending into left superior pulmonary vein (arrow), corresponding to residual malignant atrial tumor. Metastatic activity in left axillary lymph node (arrow head) is also visible. The midline shows metabolically active sternotomy scar suggestive of inflammation.

A subsequently performed whole body positron emission tomography (PET) scan with F¹⁸ – fluorodeoxy glucose revealed an area of abnormal tracer activity in a soft tissue mass occupying entire left superior pulmonary vein and encroaching into adjacent LA wall (Fig. 1F – large arrow). A one month later performed PET scan showed a single pulmonary nodule with abnormal tracer activity abutting the left superior pulmonary vein, suggesting vein erosion and access into cardiac chamber (Fig. 1G and H). It is noteworthy that this nodule was not visualized in previous scan. There was no other hypermetabolic lesion in rest of the lungs. Interestingly, another focus of increased radiotracer activity was found in ascending aorta suggesting tumor embolization (Fig. 1F – small arrow). The whole right breast and right axilla were free of malignant activity; however, two left axillary lymph nodes revealed hypermetabolic lesions (Fig. 1H). In addition, there was a small subcutaneous lesion in right anterior abdominal wall (Fig. 1H).

Cystosarcoma phyllodes, is a rare, locally aggressive and recurrent tumor accounting for approximately 1% of breast tumors. While metastases to heart are uncommon, cardiac involvement is known.² The pathways of metastatic invasion of heart in descending order of frequency are tumor embolization through veins, hematogenous spread, lymphatic spread and direct invasion.³ Although relatively rare, hematogenous metastasis is associated with poor prognosis.⁴ Other rare presentations of this tumor are RV metastasis causing pulmonary embolism, RVOT obstruction⁵ or even cardiogenic shock.⁶

The present case is interesting for many reasons. First, Cystosarcoma Phyllodes metastasizing to heart is a rare entity. Secondly, the tumor presented as a substantially large intracavitary cardiac mass causing decompensation and significant immediate risk potential, without easily recognizable involvement of other anatomically related structures to explain the route of metastasis. In this case the metastatic lesions of lung and mediastinum were too small to be detected even by CT scan at the time of diagnosis of cardiac tumor and could be detected only by increased metabolic activity on PET scan. In all other cases reporting pulmonary vein invasion from mediastinum, the primary tumor was large enough to explain local invasion, before extending into the pulmonary vein.⁷ Thirdly, although extension of metastases into the left atrium by invasion of the pulmonary veins is well documented for primary pulmonary malignancies, this phenomenon is uncommon for lung or mediastinal metastatic lesions.⁴

In our case, the probable route of metastases was hematogenous into the contra lateral axillary lymph nodes, lung and mediastinal lymph nodes. From the latter, it invaded directly through the left superior pulmonary vein. Malignant phyllodes are known to metastasize by the hematogenous route rather than lymphatic. This also explains the reason for negative nodes on initial axillary dissection.

Cardiac metastases are rare but important cardiovascular diagnoses. Their potentially lethal course and the possibility of avoiding major complications with excision, make their diagnosis consequential. Malignant tumors may reach heart through atypical routes. Strategic strong index of suspicion and thorough investigation of every case may avoid missing the diagnosis.

Conflicts of interest

All authors have none to declare.