Myofibroblastoma of the breast

A myofibroblastoma is one of a group of ‘soft-tissue‘ tumors which can arise out of the ‘stromal‘ elements in breast tissue.

Myofibroblastomas are considered to be benign tumors, and they are somewhat more common in older men than in women.

Myofibroblastomas are also sometimes called ‘myogenic stromal tumor‘, and can occur in many ‘soft tissue‘ areas of the body including:-

the breast
skin
lymph nodes
suprasellar regions of the brain.

The only real concern with myofibroblastoma is that it has certain histological/microscopic features which can ‘mimic‘ spindle cell carcinoma of the breast, which is a more serious, malignant condition.

The ‘myofibroblasts‘ which comprise the tumor have a particular visual appearance; a ‘spindle-like cell‘.

Certain malignant breast cancer cells also have this ‘spindle-cell‘ appearance, so they can be confused or even misdiagnosed, but myofibroblastoma is not associated with spindle cell carcinoma at all.

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Slow growing, often discovered as a painless lump

A myofibroblastoma is often discovered clinically as a ‘painless lump‘.

They are very slow-growing tumors, but they can actually become very large.

They will also show up on a screening mammogram. Usually, they are less than 4 cm in diameter when discovered on a breast X-ray.

Myofibroblastomas are extremely rare. They tend to develop in the 40-80 year age range, with an average age around 65.

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Other soft tissue tumors sharing morphological features with myofibroblastoma

Myofibroblasts are present in very small numbers in all tissues, but when they grow in a new and unexpected way (neoplasm) it becomes a lesion or tumor, (i.e. myofibroblastoma)

Myofibroblastomas share many features with other soft tissue neoplasms such as:-

Differences tend to be based on:-

the presence of various protein secretions
cellular activity
atypia
presence of vascular elements
the density of the various elements.

What do the terms ‘myo’ and ‘fibroblast’ mean?

The term ‘myo‘ refers to muscle, and in the case of breast myofibroblastoma, it refers to the muscle cells (smooth muscle or SM) found in the wall of breast ducts or in the wall of arterioles.

‘Blastoma‘ refers to a cell which has not fully evolved or ‘differentiated’ into a mature cell; either a mature muscle cell or a fibroblast.

A ‘fibroblast‘ is a type of cell that is most common in connective tissues. They synthesize the extracellular matrix and collagen and form into structural-supportive elements (stroma), upon which organs and glands develop.

Fibroblasts are also very important in the ‘wound-healing‘ process. Fibroblasts help maintain the structural integrity of connective tissue by constantly secreting undifferentiated genetic ‘precursors‘ of the extracellular matrix.

This ‘extracellular matrix‘ is essentially the ‘ground substance‘ from which many different fibers associated with various connective tissues arise.

Breast myofibroblastoma cells have characteristics of smooth muscle cells and fibroblasts

So, this ‘combination‘ term; ‘myo-fibroblast-oma‘ , means that a tumor (oma) has formed out of these immature-undifferentiated cells which have features and characteristics BOTH of smooth muscle cells (SM… ‘myo’) and fibroblasts.

A ‘Myofibroblast‘ is a cell that is in between a smooth muscle cell and a fibroblast in differentiation.

The mammographic appearance of myofibroblastoma

Myofibroblastomas can present with a variety of appearances on a mammogram, but typically they are homogeneous, well-circumscribed and lobulated lesions.

They usually have no microcalcifications. Ultrasound is not that useful in diagnosing a myofibroblastoma, as they cannot usually be differentiated from breast fibroadenomas.

The ultrasound image below shows a solid nodule with smooth, benign-appearing margins.

Statistically, it is far more likely to be a fibroadenoma, but this is, in fact, a myofibroblastoma.

Histological features of myofibroblastoma

Myofibroblastomas will typically have well-circumscribed margins.

The makeup of the tumor cells can be quite varied; they tend to mostly show spindle-shaped cells, but can also contain round, polygonal, or ‘epithelioid‘ cells.

Variable amounts of collagen and adipose tissue may also be present. A known variant of myofibroblastoma is the ‘Epithelioid-cell‘ myofibroblastoma which contain a majority of cells with an epithelioid morphology, which is even more apt to be confused for malignant carcinoma.

Mitoses and necrosis are generally not evident

Myofibroblastomas show virtually no necrosis and tend not to feature mitosis or ‘cell division‘.

Vascular elements (blood supply) are also not characteristic. (Some of the other related soft tissue tumors do feature a little more necrosis, mitosis, or vascular elements.)

But the main diagnostic aspect which readily identifies myofibroblastoma is that they stain for certain proteins which are characteristic of ‘muscle‘ related activity.

The positive staining for the ‘CD34‘ protein, desmin and vimentin tends to point to a myofibroblastoma differentiation.

Treatment of myofibroblastoma of the breast

Usually, a myofibroblastoma will be treated by local surgical excision, and that takes care of it.

The main concern surrounding myofibroblastoma in the breast is that clinical, radiological, and cytological findings are fully evaluated and reconciled to confirm the differential diagnosis.

If specialists conclude that the tumor is a true myofibroblastoma and does not represent spindle cell carcinoma or perhaps another breast carcinoma with the incidental presence of myofibroblasts, there really is no need for additional measures aside from a routine follow up after a year or two.

There are no recurrences or metastis of myofibroblastoma in the known literature.

Can myofibroblasts occur in other benign or possible malignant breast tumors?

Myofibroblasts do in fact occur in other tumors. They are common in other benign soft tissue tumors such as:-

But, they can also occur in various sarcomas and in metaplastic breast carcinoma.

Increased amounts of mitotic activity, cellular pleomorphism (odd shapes) and infiltrative margins, will tend to point to a more malignant diagnosis of possible metaplastic breast carcinoma myofibroblastic sarcoma.

The presence of myofibroblasts within breast carcinoma can affect prognosis

A myofibroblastoma is a benign tumor comprised mainly of these myofibroblasts, or these immature ‘spindle‘ appearing cells.

But when a breast carcinoma is already confirmed and some of these myofibroblasts seem to be part of the situation, that can affect the behavior of the tumor and the prognosis.

In a malignant situation, it is difficult to predict the interaction of all the different proteins and hormones within the ‘intercellular matrix‘.

Fibroblasts can have both an inhibitory and a stimulating effect on tumor growth.

At the same time, the presence of myofibroblasts which test positive for smooth muscle actin (SMA) is sometimes associated with tumors more prone to invasion.

Recent studies now suggest that the presence of myofibroblasts in the tissues of invasive ductal carcinomas tends to suggest a more unfavourable prognosis.

Here are some Q&A’s…

What is the Treatment for Myofibroblastoma?

Surgical excision.

What are the myofibroblastoma symptoms?

These tumors are painless, slow growing masses.

What are the myofibroblastoma breast pathology outlines?

Consists of bland spindle cells arranged in fascicles with interspersed thick bundles of collagen. They typically stain with CD34 and desmin.

What is myofibroblastoma diagnosis?

The diagnosis is based on examination under a microscope. Findings may be suggestive.

What kind of tumor is myofibroblastoma?

It is a benign tumor.

References

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