Phyllodes tumour of the breast

Overview

A phyllodes tumour (also spelled phyllodes tumor) is a rare type of breast lump that develops in the connective (stromal) tissue of the breast, rather than in the ducts or milk-producing glands where most breast cancers begin. It belongs to a group of growths known as fibroepithelial tumours, which also includes the much more common fibroadenoma.

The name comes from the Greek word “phyllon”, meaning leaf, because the tumour forms distinctive leaf-like projections when examined under a microscope. In older medical literature you may still encounter the outdated name cystosarcoma phyllodes — a misleading term, since most phyllodes tumours are not cancerous.

What makes this condition unusual is its wide spectrum of behaviour. Some phyllodes tumours are completely benign and never spread, some have features “in between” (borderline), and a smaller proportion are malignant and can behave like a soft-tissue sarcoma. Even benign tumours can grow quickly and, if not fully removed, may come back (recur). This is why accurate diagnosis and complete surgical treatment matter so much.

Having a phyllodes tumour does not automatically mean you have cancer. Most are benign. However, all phyllodes tumours require specialist assessment and usually surgery.

How Common Is It? Who Is Affected?

Phyllodes tumours are rare. They account for:

• Less than 1% of all breast tumours (roughly 0.3–1%)
• Approximately 2–3% of all fibroepithelial breast tumours

Who typically develops them:

• Most commonly women between 35 and 55 years of age (benign tumours usually appear slightly earlier, around the late 30s to early 40s; malignant ones on average in the mid-40s)
• Occasionally teenagers and younger women — in this group the tumours are usually benign
• Very rarely men, usually in the context of gynaecomastia (male breast tissue enlargement)

Some studies suggest phyllodes tumours may occur slightly more often in certain populations, including women of Asian and Latin American descent, and that patients in these groups may present at a younger age.

Types and Grading of Phyllodes Tumours

Unlike ordinary breast cancer, which is staged, phyllodes tumours are graded by pathologists according to how the cells look and behave under the microscope. The World Health Organization (WHO) recognises three categories:

Pathologists assign a grade by assessing several microscopic features together:

• Cellularity – how densely packed the cells are in the connective tissue (stroma)
• Atypia (pleomorphism) – how abnormal the individual cells look
• Mitotic activity – how many cells are actively dividing (counted per 10 high-power microscope fields)
• Tumour margins – whether the edges are well-defined (pushing) or infiltrating into nearby tissue
• Stromal overgrowth – whether the connective tissue component dominates over the glandular component
• Heterologous elements – rarely, malignant tumours contain other tissue types (e.g., bone, fat or cartilage-forming cells)

How Does It Look?

Because people often first notice this condition themselves, it helps to understand how a phyllodes tumour looks and behaves at every level — on the body, on scans, and under the microscope.

On the body (what you can see and feel)

• A solid, firm, round or oval lump in the breast that is usually mobile under the fingers — it can often be moved slightly rather than feeling fixed
• Typically well-defined edges, so it may feel like a smooth “marble” or “grape” under the skin
• Size at diagnosis is usually 4–5 cm, substantially larger than the average fibroadenoma
• In some cases the tumour grows to 10 cm or more; masses of 20–30 cm have been reported. Very large tumours are sometimes described in the media as “giant phyllodes tumours”
• As the tumour enlarges it can stretch the overlying skin, making it appear:
• shiny and tight
• thinned
• crossed by prominent, engorged veins
• With very large tumours the breast may become visibly enlarged, heavy or distorted compared with the other side
• In neglected or extremely large cases, pressure on the skin can cause ulceration — notably, even benign tumours can ulcerate purely through pressure, so skin breakdown does not automatically mean cancer
• The lump can occur in either breast, most often in the upper outer portion; both breasts being affected at once is uncommon

On imaging

Important: no scan can reliably tell a phyllodes tumour apart from a fibroadenoma. Only a tissue diagnosis (biopsy) — and ideally examination of the entirely removed tumour — confirms the diagnosis and its grade.

Under the microscope

• The tumour has a characteristic leaf-like (fronded) architecture: elongated clefts lined by normal breast ducts, into which cellular stromal projections bulge — like leaves growing into hollow spaces
• The connective tissue component is more cellular than in a fibroadenoma
• In malignant tumours the stromal cells look markedly abnormal, divide rapidly, and may overrun the glandular part entirely
• On the cut surface of a removed specimen, the tumour appears as a bulky, firm, pale-grey to whitish mass with visible slit-like clefts and cysts — the gross equivalent of the microscopic “leaves”

Symptoms

Phyllodes tumours often produce surprisingly few symptoms relative to their size. The most characteristic features are:

Most common symptoms

• A painless breast lump — this is the presenting complaint in the great majority of patients
• Rapid growth: the lump often noticeably increases in size over weeks to months. A history of fast, sustained growth in a previously stable lump is one of the strongest clinical red flags for a phyllodes tumour
• A sense of fullness, heaviness or tension in the breast as the mass enlarges
• Skin changes over the lump: tight, shiny skin and enlarged visible veins
• Visible change in breast size or shape with larger tumours

Less common symptoms

• Skin ulceration or bleeding over very large tumours
• Discomfort or pain (unusual, but possible as the tumour stretches tissue)
• Nipple discharge — rarely reported and not typical

What is usually NOT seen

• Swollen lymph nodes under the arm are rarely enlarged, even with malignant tumours, because phyllodes tumours spread through the bloodstream, not the lymphatic system
• General symptoms such as weight loss or fatigue are uncommon unless there is advanced metastatic disease

A practical warning sign: if you have (or previously had) a breast lump that was thought to be a fibroadenoma and it suddenly starts growing quickly**, ask your doctor about the possibility of a phyllodes tumour. Adult women with “new fibroadenomas” over the age of 30–35 are often biopsied for exactly this reason.

Causes and Risk Factors

The exact cause of phyllodes tumours is unknown. Research has identified some associations:

• Hormonal influences — oestrogen appears to play a role in growth, as the tumours occur almost exclusively in women and can grow during puberty or pregnancy
• Genetic changes — tumour cells frequently show specific alterations, for example in the MED12 gene and in pathways controlling cell division (e.g., TERT promoter, p53 in malignant cases); these changes are found in the tumour itself, not usually inherited
• Previous breast conditions — some patients have a history of fibroadenomas, and in a small number of cases a phyllodes tumour appears to develop within one, although the exact relationship is debated
• Li-Fraumeni syndrome — a rare inherited cancer predisposition syndrome has been associated with a higher risk of phyllodes tumours
• Trauma, breast implants and lactation have occasionally been suggested as factors, but no firm link has been proven

There are no well-established lifestyle or dietary risk factors, and nothing reliable you can do to prevent the condition.

Diagnosis

Diagnosing a phyllodes tumour can be genuinely challenging. It mimics fibroadenoma on examination and imaging, and even needle biopsies can be inconclusive. The standard pathway includes a “triple assessment”:

Step 1 — Clinical examination

A doctor palpates the breast, assesses size, mobility, skin changes and lymph nodes, and asks about the speed of growth.

Step 2 — Imaging

• Ultrasound — first choice in women under ~35–40 and as an adjunct at any age
• Mammography — typically in women over 35–40
• MRI — occasionally, mainly for surgical planning of large masses

Step 3 — Tissue sampling

• Core needle biopsy — the preferred first-line test; it takes a small cylinder of tissue and is far more informative than fine-needle aspiration (FNA), which is often insufficient to distinguish phyllodes tumours from fibroadenomas
• Even core biopsies can be inconclusive; if suspicion persists, an excisional biopsy (complete removal of the lump) provides the definitive answer

Additional tests (when malignant disease is suspected)

• Chest X-ray or CT scan of the chest — because the lungs are the most common site of spread
• Bone scan or further imaging only if symptoms suggest it

Final grading is always made by the pathologist on the entire removed tumour, looking at the whole area with the most abnormal features.

Treatment

The mainstay of treatment for every phyllodes tumour — benign, borderline or malignant — is complete surgical removal with clear margins.

Surgery

Incomplete removal with narrow margins is the single biggest predictor of the tumour growing back.

Radiotherapy

• Not routinely recommended after complete excision of benign tumours
• Often considered for malignant (and selected borderline) tumours, after mastectomy for large tumours, or for recurrences — evidence suggests it reduces the risk of local recurrence
• Decided case-by-case, weighing benefits against side effects

Chemotherapy and other drug treatments

• No routine role for benign or borderline tumours
• May be offered for metastatic or inoperable malignant disease, usually with regimens borrowed from soft-tissue sarcoma treatment (e.g., doxorubicin-based therapy)
• Hormone therapy (e.g., tamoxifen) is ineffective — although the tumour’s ducts may contain hormone receptors, the driving force is the stromal component, which does not respond
• Targeted drugs and clinical trials may be options in advanced disease

Can small, benign-appearing tumours just be monitored?

In selected cases — a small lesion, benign on good-quality biopsy, confirmed by a specialist multidisciplinary team — careful surveillance is sometimes discussed. However, because biopsies can miss higher-grade areas and even benign tumours tend to grow, most guidelines still favour complete excision. This decision should always be individualised.

Prognosis, Recurrence and Follow-up

The outlook depends mainly on the grade of the tumour and whether it was completely removed.

Local recurrence (regrowth in the breast) — approximate figures

Recurrences typically appear within the first 2–3 years after surgery and are treated with further surgery, sometimes plus radiotherapy. Occasionally a recurrent tumour has a higher grade than the original.

Distant spread (metastasis)

• Occurs almost exclusively with malignant tumours (in roughly 10–25% of malignant cases; borderline very rarely)
• Spreads via the bloodstream — the lungs are by far the most common site, followed by bone; liver and brain metastases are less frequent
• Metastatic disease is difficult to treat and carries a guarded prognosis

Follow-up

There is no single universal schedule, but typical practice includes:

• Clinical examinations every 3–6 months for the first 2–3 years, then less frequently
• Breast imaging (ultrasound and/or mammogram) at regular intervals
• For malignant tumours, periodic chest imaging is often recommended
• Life-long breast awareness: knowing how your chest normally looks and feels, and reporting any change promptly

Living With the Diagnosis — Practical Points

• A diagnosis of a phyllodes tumour is not the same as a diagnosis of breast cancer, and treatment lines differ significantly — make sure your case is discussed in a multidisciplinary breast team or specialist sarcoma unit if malignant
• Ask your pathologist or surgeon about the reported grade and margin status — these two pieces of information drive everything that follows
• Even after successful treatment, stay breast-aware and keep follow-up appointments, because recurrence is possible
• Large tumours and mastectomy can affect body image and emotional wellbeing — psychological support and specialist breast-care nurses are a valuable part of care
• Pregnancy, breastfeeding and most normal activities are possible after treatment; discuss personal circumstances with your team

When to See a Doctor

Contact your GP or breast clinic promptly if you notice:

• Any new lump in the breast
• A known lump that is growing quickly
• Change in size, shape or symmetry of one breast
• Skin that looks tight, shiny, reddened or ulcerated, or newly prominent veins over the breast
• Any lump returning after previous breast surgery

Early assessment of a growing lump leads to smaller, easier operations and better cosmetic outcomes.

Key Takeaways

1. Phyllodes tumours are rare fibroepithelial breast tumours found mostly in women aged 35–55.
2. They are graded as benign, borderline or malignant — most are benign.
3. The typical picture is a painless, well-defined lump that grows rapidly.
4. No scan can reliably distinguish them from fibroadenomas — biopsy and, ultimately, examination of the whole specimen is required.
5. Treatment is surgical removal with clear margins; lymph node removal and hormone therapy are generally unnecessary.
6. Recurrence is possible at any grade, so structured follow-up matters.
7. Malignant tumours can spread, chiefly to the lungs, and require specialist care.

References

Gnerlich, J.L., Williams, R.T., Yao, K., Jaskowiak, N. and Kulkarni, S.A. (2014) ‘Utilization of radiotherapy for malignant phyllodes tumors: analysis of the National Cancer Data Base’, Annals of Surgical Oncology, 21(4), pp. 1222–1230.

Mishra, S.P., Tiwary, S.K., Mishra, M. and Khanna, A.K. (2013) ‘Phyllodes tumor of breast: a review article’, ISRN Surgery, 2013, Article 361469.

National Comprehensive Cancer Network (NCCN) (2023) NCCN Clinical Practice Guidelines in Oncology: Breast Cancer — Phyllodes Tumor. Plymouth Meeting, PA: NCCN.

Reinfuss, M., Mituś, J., Duda, K., Stelmach, A., Ryś, J. and Smolak, K. (1996) ‘The treatment and prognosis of patients with phyllodes tumor of the breast: an analysis of 170 cases’, Cancer, 77(5), pp. 910–916.

Tan, B.Y., Acs, G., Apple, S.K., Badve, S., Bleiweiss, I.J., Brogi, E., Calvo, J.P., Dabbs, D.J., Ellis, I.O., Eusebi, V., Farshid, G., Fox, S.B., Ichihara, S., Lakhani, S.R., Rakha, E.A., Reis-Filho, J.S., Richardson, A.L., Sahin, A., Schmitt, F.C., Schnitt, S.J., Siziopikou, K.P., Soares, F.A., Tse, G.M., Vincent-Salomon, A. and Tan, P.H. (2016) ‘Phyllodes tumours of the breast: a consensus review’, Histopathology, 68(1), pp. 5–21.

World Health Organization (2019) WHO Classification of Tumours: Breast Tumours. 5th edn. Lyon: International Agency for Research on Cancer (IARC).

Zhang, Y. and Kleer, C.G. (2016) ‘Phyllodes tumor of the breast: histopathologic features, differential diagnosis, and molecular/genetic updates’, Archives of Pathology & Laboratory Medicine, 140(7), pp. 665–671.

Cancer Research UK (n.d.) Phyllodes or phylloides breast tumours. Available at: https://www.cancerresearchuk.org (Accessed: 2024).

American Cancer Society (2022) Phyllodes Tumors of the Breast. Atlanta, GA: American Cancer Society.