Symptoms and Causes of Phyllodes Tumors

Growing in a “leaf-like” pattern, from which they acquired their name, phyllodes tumors (PTs) are fibroepithelial tumors of the breast. They may occur at any age, but occur primarily in women between 40 to 60 years old and are extremely rare in men.

They make up less than 1% of all breast tumors, and may be benign or malignant in nature. Most PTs have benign characteristics, and these are typically diagnosed at a younger age than for carcinomas of the breast. Malignant tumors are diagnosed later, and account for roughly 15% of these fibroepithelial tumors.


A lump in the breast, discovered on examination by a healthcare professional or by the patient, is the most common sign of PTs. These tend to increase rapidly in size. This growth may happen over the span of a few weeks or months. While the rapid increase in size may be worrisome, it does not necessarily mean that the tumor is malignant in nature. This is especially true considering the fact that many PTs grow quickly. The lumps have a firm, well-demarcated and mobile texture. Moreover, they are painless.

The skin overlying large tumors may become bluish due to the dilations of veins, but unlike breast carcinoma, nipple retraction is rare. PTs tend to occur mostly in the upper outer quadrant of the breast. Rarely, they present bilaterally. The average tumor size is around 5 cm, but any of these tumors may grow up to several times larger, with one being reported to have been 40 cm in diameter. The larger the tumor, the greater the chances are that it will produce a visible bulge under the skin. Skin ulceration, although uncommon, may occur. Patients with metastases to the lungs, the most frequent site, may present with dyspnea, or trouble with breathing. Other signs of metastasis include bone pain and fatigue.


The exact etiology of PTs and their relationship to fibroadenomas (a type of benign breast lesion) remains unclear at the moment. PTs are more common in women with fibroadenomas. An important finding, however, is that most women with fibroadenomas do not go on to develop PTs.

PTs, unlike breast carcinomas, tend to originate in the stroma of the breast. The stroma is the  connective tissue which contains fat tissue and ligaments that surround the lobules and ducts, as well as the lymph and blood vessels that make up the breast. PTs are composed predominantly of stromal cells, and may also contain ductal and lobular cells.

Some studies have shown that fibroadenomas have polyclonal elements, and therefore these tumors should be classified as hyperplastic as opposed to neoplastic lesions. It has been further suggested that some fibroadenomas are characterized by somatic mutations which result in monoclonal expansion. This type of fibroadenoma cannot be distinguished histologically from the polyclonal counterpart. However, these monoclonal proliferations are more likely to recur locally and may progress to PTs, a hypothesis which is supported by clonal analysis.  

There are other studies that have postulated that growth factors produced by breast epithelium may lead to the stromal induction of PTs. Factors that have been implicated in the stimulation of tumor growth include increased estrogen activity, lactation, pregnancy and trauma. The exact mechanisms by which these factors stimulate growth is not clear. However, it is believed that a stimulator of breast fibroblast growth, endothelin-1, may be heavily involved.


Further Reading

Last Updated: Jan 2, 2023

Dr. Damien Jonas Wilson

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Dr. Damien Jonas Wilson

Dr. Damien Jonas Wilson is a medical doctor from St. Martin in the Caribbean. He was awarded his Medical Degree (MD) from the University of Zagreb Teaching Hospital. His training in general medicine and surgery compliments his degree in biomolecular engineering (BASc.Eng.) from Utrecht, the Netherlands. During this degree, he completed a dissertation in the field of oncology at the Harvard Medical School/ Massachusetts General Hospital. Dr. Wilson currently works in the UK as a medical practitioner.


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