What is a spindle cell lesion?


A spindle cell lesion is a descriptive term used by pathologists to describe a tissue sample containing spindle-shaped cells. These are cells that are longer than they are wide and resemble elongated ovals, thin cigars, or grains of rice when viewed under the microscope. Spindle-shaped cells are normally found in many connective tissues, including muscle, fibrous tissue, blood vessel walls, and the supporting tissue found throughout the body.

The term spindle cell lesion does not describe a specific disease. Instead, it describes the appearance of the cells, which can be seen in a wide range of conditions. Some spindle cell lesions are harmless, while others represent serious cancers. Because of this, the term is often used when more information is needed before a final diagnosis can be made.

Why might my pathology report use this term?

Pathologists often use the term spindle cell lesion in biopsy reports when only a small sample of tissue is available or when the features seen under the microscope overlap among many possible conditions. In these situations, it is not yet possible to tell whether the lesion is benign, reactive, or malignant.

Using this general term allows your healthcare team to continue evaluating the tumour while additional tests are performed. A more specific diagnosis is usually provided once those test results are available or once more tissue is examined.

Where are spindle cell lesions found?

Spindle cell lesions can develop almost anywhere in the body because spindle-shaped cells are found in so many normal tissues. Common locations include:

  • Skin and soft tissue.

  • Breast.

  • Lungs and pleura.

  • Digestive tract.

  • Genitourinary tract.

  • Head and neck region.

Finding a spindle cell lesion in one of these areas does not by itself indicate cancer. The final diagnosis depends on the results of additional testing and the tumour’s microscopic features.

Are spindle cell lesions cancer?

Not always. A spindle cell lesion describes how the cells look, not whether the lesion is benign or malignant. Spindle cells can appear in harmless growths, reactive or inflammatory conditions, and aggressive cancers. Because the appearance alone is not enough to determine the exact diagnosis, pathologists often need more tissue or additional testing.

Types of spindle cell lesions

Benign (non-cancerous) spindle cell tumours

These noncancerous spindle cell lesions do not spread to other parts of the body and usually behave in a slow, predictable manner.

Examples include:

  • Fibroma: A benign tumour of fibrous tissue that usually grows slowly.

  • Leiomyoma: A smooth muscle tumour commonly found in the uterus, digestive tract, or skin.

  • Schwannoma: A tumour arising from cells that cover nerves. It is typically painless and slow-growing.

  • Neurofibroma: A benign tumour involving peripheral nerves. It may occur alone or as part of neurofibromatosis type 1.

  • Nodular fasciitis: A rapidly growing but benign lesion of fibrous tissue that can look concerning but often resolves completely after removal.

Reactive or inflammatory spindle cell lesions

Some spindle cell lesions are not tumours at all. Instead, they represent the body’s response to injury, infection, inflammation, or healing. Examples include scar tissue, granulation tissue, and changes seen after surgery or trauma.

Malignant (cancerous) spindle cell tumours

Some spindle cell lesions represent cancer. These tumours can grow quickly and may spread to other parts of the body.

Examples include:

  • Leiomyosarcoma: A cancer of smooth muscle that may develop in the uterus, digestive tract, or large blood vessels.

  • Undifferentiated pleomorphic sarcoma: A high-grade soft tissue cancer with very abnormal spindle-shaped cells.

  • Spindle cell squamous cell carcinoma: A subtype of squamous cell carcinoma in which the cancer cells appear spindle-shaped.

  • Spindle cell melanoma: A type of melanoma in which the tumour cells develop a spindle shape.

  • Other cancers with spindle features: Some cancers, such as renal cell carcinoma or mesothelioma, may develop spindle-shaped areas and require special testing to identify.

Because so many possible tumours can have spindle-shaped cells, additional testing is almost always needed to determine the exact diagnosis.

How do pathologists determine the exact diagnosis?

To classify a spindle cell lesion more precisely, pathologists rely on a combination of microscopic findings, special stains, and molecular tests.

They consider the following:

  • Microscopic appearance: Pathologists examine the shape of the cells, their arrangement, the rate at which they divide, and whether they are invading nearby tissue.

  • Immunohistochemistry: This test uses special stains to highlight proteins in cells, helping identify their origin. For example, cytokeratins suggest carcinoma, while S100 or SOX10 suggest melanoma or a nerve sheath tumour.

  • Molecular tests: Some spindle cell tumours have characteristic genetic mutations or rearrangements, and detecting these changes helps confirm the diagnosis.

  • Clinical and imaging findings: Information about the size, location, and behaviour of the lesion also helps narrow down the possibilities.

By combining all of these findings, the pathologist can usually determine whether the spindle cell lesion is benign, malignant, or reactive and can identify the specific tumour type.

Why is identifying the specific tumour type necessary?

Different spindle cell tumours behave very differently. Some are slow-growing and require only observation or simple surgical removal, while others are aggressive cancers that require chemotherapy, radiation, or targeted therapy. Knowing the exact tumour type helps your doctor:

  • Understand how the tumour is likely to behave.

  • Choose the most effective treatment.

  • Estimate the prognosis.

  • Decide whether additional testing, surgery, or follow-up is needed.

A clear and specific diagnosis also helps avoid unnecessary treatment for benign or reactive conditions.

Questions to ask your doctor

  • Do we have enough information to know whether the lesion is benign or malignant?

  • Were immunohistochemistry or molecular tests performed?

  • Do I need additional imaging or a larger biopsy to complete the diagnosis?

  • What are the possible tumour types that fit the current findings?

  • What are the next steps for diagnosis, monitoring, or treatment?

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