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Everything You Need to Know About Mohs Micrographic Surgery and Mohs Histology

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mohs histology

Have been diagnosed with skin cancer? Or, perhaps, you just want to learn more about Mohs histology? You may be wondering about your treatment options and what to expect. Here at Dermatology and Skin Health, we specialize in Mohs micrographic surgery, an advanced treatment for removing certain types of skin cancer

In this article, we will provide an in-depth explanation of Mohs surgery and the vital role played by Mohs histology. We will overview the Mohs procedure, discuss the significance of Mohs histology, describe the histology technique, and answer common questions patients have about this specialized surgical method. 

What is the Mohs procedure in dermatology, and why is it important?

Mohs surgery is a technically precise surgical technique used to treat common types of skin cancer. It offers the highest cure rates and minimizes the chance of recurrence. 

A study published in the National Center for Biotechnology Information (NCBI) explains that Mohs surgery uses en face frozen section analysis (FSA) with complete margin examination for the excision of select basal cell carcinomas (BCC), obtaining excellent cosmetic outcomes and extremely low recurrence rates. However, Mohs with FSA is time-consuming because of the need to iteratively perform cryosectioning on sequential excisions.

With Mohs surgery, thin layers of cancerous tissue are progressively removed and examined under a microscope until only cancer-free tissue remains. This allows complete microscopic margin control during the procedure to eliminate all root traces of tumor while maximizing preservation of healthy tissue.

The unmatched precision of Mohs surgery makes it the skin cancer treatment method of choice for cancers located on cosmetically or functionally sensitive areas such as the face, ears, hands, feet, or genitals. It also has the highest success rates for high-risk skin cancer types. 

For these reasons, Mohs micrographic surgery has become the gold standard treatment for many types of skin cancer.

What is the significance of Mohs histology in dermatology?

Mohs surgery is dependent on the detailed frozen section analysis performed by the Mohs histotechnologist. After the Mohs surgeon removes a thin tissue layer, the Mohs histology technician processes and stains the tissue sample, creating frozen section slides that allow examination of 100% of the surgical margin under a microscope. 

This Mohs frozen section procedure enables the surgeon to microscopically map and precisely locate any remaining cancer cells in the tissue. This back-and-forth coordinated effort between the Mohs surgeon and Mohs histology technician of staged excision, frozen tissue preparation, microscopic analysis, and additional targeted removal is repeated until no detectable cancer cells remain.

  • A study titled "Mohs Surgery Histopathology Concordance" conducted at a single institution in the United States over a period of 10 years analyzed 1,156 slides. The study found a statistically significant concordance between Mohs surgeons and dermatopathologists in frozen section interpretation in the Mohs surgery setting. 


The success rate of the procedure was found to be dependent on accurate microscopic evaluation of carefully mapped specimens. The Mohs surgeon acts as a pathologist and is, therefore, able to translate abnormal findings on the tissue map into appropriate sequential tumor removal. The study also highlighted the critical role of the surgeon’s skill in interpreting histologic specimens.

In short, Mohs histology is vital for the success of Mohs surgery in eradicating skin cancer while maximizing the preservation of healthy tissue. Meticulous frozen section preparation, optimized staining, and expert microscopic analysis allow detailed marginal mapping and cancer localization in a way that routine surgical pathology cannot match. 

This makes Mohs histology an indispensable component of the integrated Mohs treatment process.

How does Mohs surgery relate to Mohs histology?

Mohs surgery requires the coordinated efforts of the Mohs surgeon and Mohs histotechnologist. After the surgeon precisely excises a thin skin cancer specimen layer, the Mohs histotech orients, freezes, sections, and stains the tissue sample to create microscope slides. 

These frozen section slides are then microscopically examined by the Mohs surgeon to check the deep and peripheral surgical margins for any remaining cancer cells.

If residual cancer cells are identified, their locations are mapped, and additional tissue is removed by the surgeon only from the precise areas still containing the tumor. New frozen section slides are produced and analyzed until the margins are completely free of cancer. 

Mohs surgery relies entirely on this dynamic partnership between the Mohs surgeon extracting tissue and the Mohs histology technician preparing and analyzing the corresponding frozen section slides. Their close teamwork ensures no residual tumor remains and healthy tissue is maximally conserved.

Could you describe the histology technique used in Mohs surgery?

The Mohs frozen section procedure involves multiple meticulous steps, as explained by a StatPearl resource titled “Mohs Micrographic Surgery”.

  1. The Mohs surgeon excises a thin layer of tissue.
  2. The tissue specimen is immediately brought to the Mohs histology lab.
  3. The Mohs histotech orients the tissue sample to map the precise excision borders.
  4. The tissue is rapidly frozen onto a cryostat chuck, allowing very thin slicing.
  5. The frozen tissue block is sectioned into extremely thin slices, typically 4-6 microns thick.
  6. The thin frozen sections are mounted onto glass slides.
  7. The slides are stained, usually with hematoxylin and eosin (H&E).
  8. The prepared frozen section slides are evaluated under a microscope by the Mohs surgeon while the patient waits.
  9. Additional excision layers are taken as needed, with new slides produced and analyzed after each, until the margins are cleared of any residual tumor.
  10. This specialized frozen section method enables examination of 100% of the surgical margin and allows the Mohs surgeon to definitively determine if any cancer cells remain at the edge of the excised tissue.

What does "Mohs" stand for in the context of dermatology?

In dermatology, “Mohs” refers to Dr. Frederic Mohs, the surgeon who pioneered the Mohs surgery technique in the 1930s. Dr. Mohs was a Professor of Surgery at the University of Wisconsin-Madison who specialized in the treatment of skin cancer. 

He wanted to develop a procedure that allowed meticulous microscopic control of surgical margins to ensure all roots and traces of skin cancer could be eliminated. The advanced surgical method he invented came to be known as Mohs micrographic surgery or Mohs surgery. “Mohs histology” also derives from Dr. Mohs and refers specifically to the frozen section procedure performed during Mohs surgery by Mohs histotechnicians.

By systematically excising thin layers of tissue and analyzing 100% of the deep and peripheral margins under a microscope, Dr. Mohs created a transformative surgical treatment that offered the highest cure rates for skin cancer.

What are the responsibilities of a Mohs histotech?

Mohs histotechnicians, or Mohs histotechs, play an indispensable role in Mohs surgery. They are specially trained to prepare the frozen tissue sections from Mohs cases that allow the surgeon to check for any residual tumor at the margins.

Key responsibilities include:

  • Operating the cryostat machine to freeze and slice the excised tissue samples.
  • Staining the frozen sections using hematoxylin and eosin (H&E).
  • Troubleshooting any technical issues that arise with slide preparation.
  • Precisely mapping the location and orientation of each tissue sample.
  • Thoroughly documenting details for each Mohs case.
  • Communicating with the Mohs surgeon about specimen orientation, margin status, and any other important factors.
  • Preparing the detailed frozen section slides that allow the surgeon to check for residual tumor at the margins.
  • Enabling the staged, layered surgical excisions and microscopic tumor localization that make Mohs surgery possible.

How can one become a Mohs histotech?

To become a Mohs histotech, formal training in histotechnology and certification as a histotechnician (HT) is required. Hands-on experience in a high-volume dermatopathology or Mohs frozen section laboratory helps develop the specialized skills needed. 

Hands-on experience in a high-volume dermatopathology or Mohs frozen section laboratory is always beneficial. This experience can be gained through employment in such settings, as evidenced by job postings that often require at least 1 year of Mohs/ Histotech experience in a Dermatology setting.

Many Mohs histotechs complete a 1-year Mohs surgery fellowship following histotechnology training to perfect their technique. Upon completion of a dermatology residency, a physician can apply to participate in a Micrographic Surgery & Dermatologic Oncology (Mohs) fellowship-training program. 

Qualified applicants undergo a review and selection process to obtain a 1- to 2-year fellowship position with a program accredited by the ACMS.

Expertise in precisely orienting, sectioning, and staining thin frozen tissue sections is vital. Candidates should also have exceptional documentation and mapping skills given the need to track numerous tissue samples from each Mohs case. 

Obtaining Mohs-specific histology certification (e.g. the CMMT credential) demonstrates specialized expertise. With proper training and experience, Mohs histotechs become indispensable members of the skin cancer care team.

What is the average salary of a Mohs histology technician?

Average salaries for Mohs histology technicians range from $55,000 to $90,000 annually depending on experience, certification, and geographic location. Their vital work makes the unparalleled precision and effectiveness of Mohs surgery possible.

  • According to Glassdoor, the average salary for a Mohs Histology Technician in the United States is $84,177 per year
  • Salary.com reports that the average annual salary for a Mohs Technician at US Dermatology Partners is approximately $95,773
  • On the other hand, Mobile Mohs Inc reports an average salary of $55,656 for a Histology Technician

How are Mohs histology slides prepared?

The preparation of Mohs frozen sections requires meticulous technique and coordination. After the surgeon precisely excises each layer of skin cancer tissue, the specimen is immediately brought to the Mohs histology lab. 

The Mohs histotech orients the tissue sample to map out the peripheral and deep excision edges. The tissue is then frozen rapidly on a cryostat, which allows very thin slicing. 

Frozen section slices 4-6 microns thick are then cut from the tissue block and mounted on glass slides. The Mohs frozen sections are subsequently stained, most commonly using hematoxylin and eosin (H&E). Special stains like immunoperoxidase can also be utilized as needed. 

The prepared slides are then promptly transported to the Mohs surgeon for microscopic analysis to check for any remaining cancer cells at the surgical margins while the patient waits.

What does Mohs histology involve in terms of cancer treatment?

Mohs histology allows the surgeon to definitively analyze 100% of the surgical margins to precisely guide tumor removal. By preparing frozen sections from each sequentially excised tissue layer, Mohs histotech staff enable the surgeon to microscopically map any remaining cancer cells at the periphery or base of the developing surgical defect. 

This information allows additional targeted removal of residual tumors until all margins are verified as clear of cancer. Mohs histology is thus critical for removing the entire skin cancer tumor while maximizing the preservation of healthy tissue surrounding the cancer. It facilitates unparalleled precision and effectiveness in treating complex or high-risk skin cancers.

Can you explain why Mohs surgery is considered necessary?

Several key factors make Mohs surgery the treatment of choice for many skin cancers, as reported by SkinCancer.org:

  • Highest cure rates of any skin cancer treatment (up to 99% 5-year cure rate)
  • Lowest recurrence rates by allowing complete microscopic margin control
  • Maximum preservation of healthy tissue by conserved tumor removal
  • Ideal for cosmetically/functionally critical areas like the face or fingers
  • Ability to precisely examine 100% of surgical margins (not just samples)
  • Integrated, coordinated excision-histology technique
  • Can treat larger, deeper, high-risk, or recurrent tumors
  • Corrects microscopic extensions invisible to the naked eye

A study conducted in Scandinavia from 1993 to 2003 examined the 5-year recurrence rates of 587 aggressive and/or recurrent facial basal cell carcinomas treated with Mohs micrographic surgery. 

The study found that the 5-year recurrence rates were 2.1% for primary (previously untreated) tumors and 5.2% for recurrent basal cell carcinomas. This supports the claim that Mohs surgery has high success rates, particularly for high-risk skin cancer types.

For these reasons, Mohs surgery provides the most precise and effective approach to eliminating complex skin cancers while sparing the surrounding healthy tissue as much as possible. It has become the gold standard treatment for high-risk skin cancer types such as squamous cell carcinoma and melanoma.

What are the characteristics of squamous cell carcinoma histology?

Under the microscope, squamous cell carcinoma is characterized by irregular nests and cords of atypical, hyperchromatic keratinocytes extending outward from the epidermis. Abnormal keratin pearl formation, dyskeratosis, and increased mitotic figures are also typically seen. 

The acantholytic variant shows a loss of adhesion between keratinocytes. The spindle cell variant is composed of atypical spindle-shaped cells with less keratinization. A brisk inflammatory response is often present as well. 

A study by Quaedvlieg et al. found that metastatic SCCs typically have a tumor width of at least 15 mm, a vertical tumor thickness of at least 2 mm, and less differentiation.

These classic histologic features allow squamous cell carcinoma to be differentiated from other skin cancer types. Mohs surgery is considered the treatment of choice for squamous cell carcinoma located in high-risk areas.

What is Mohs cancer, and how is it treated?

In dermatology, “Mohs cancer” refers to skin cancers that are treated with Mohs surgery. The cancers most commonly treated with Mohs surgery include basal cell carcinoma and squamous cell carcinoma, which are the two most common types of skin cancer. 

Mohs surgery is also utilized for malignant melanoma, dermatofibrosarcoma protuberans, and atypical fibroxanthoma. Treatment involves staged surgical excision of cancerous tissue layers, with frozen section microscopy performed after each stage to check for residual tumors at the margins. 

This cycle continues until negative margins are achieved, allowing complete cancer removal. The subsequent surgical defect is then repaired.

Is Mohs considered a surgical procedure?

Yes, Mohs surgery is absolutely considered a surgical procedure. In fact, it is a highly complex and advanced surgical technique that requires extensive additional training beyond the dermatology residency. Like any surgery, it requires anesthesia, surgical supplies, and a sterile surgical environment.

Does a Mohs procedure cause discomfort or pain?

The surgical excisions performed during Mohs surgery typically cause only mild discomfort but are not usually very painful. A local anesthetic is injected to numb the area around the tumor before surgical excision begins. 

During the procedure, patients may feel some pressure or tugging as tissue layers are removed but should not experience significant pain. Mild soreness, swelling, and bruising can occur after surgery and may last 1-2 weeks as the wound heals. 

Compared to recovery after larger resections without frozen section control, the Mohs procedure provides excellent pain control with minimal postoperative discomfort.

The University of Rochester Medical Center also supports the claim that most patients experience only mild discomfort following Mohs Surgery. The level of discomfort depends on the size and location of the wound. Most patients manage well with over-the-counter pain relievers like acetaminophen (Tylenol) or ibuprofen (Advil, Motrin).

How long does it typically take to recover from Mohs surgery?

Recovery time after Mohs surgery depends largely on the size of the surgical defect and the repair technique used. Very small excisions may heal within 7-10 days with proper wound care. Larger defects that require complex repairs with flaps or skin grafts can take 4-6 weeks for the site to fully heal. 

Temporary swelling, bruising, and mild discomfort are common during the first 1-2 weeks after surgery. Strenuous activity should be avoided initially to protect the healing wound. 

Overall, Mohs defects tend to heal faster and with superior cosmetic outcomes compared to conventional excisions or resections. Most patients are able to resume normal activities within a couple weeks.

Are there travel jobs available in Mohs histology?

Yes, some Mohs histology technologists work as traveling contractors, filling temporary vacancies at different Mohs surgery clinics, as confirmed by Indeed. This allows flexibility to gain experience at diverse practices across a region while enjoying location variety. 

Traveling Mohs histotechs may be independently contracted or employed by staffing agencies that place them on assignment where needed. Contract durations range from a few days to several months based on the practice’s needs. 

Travel can provide valuable exposure to different equipment, protocols, and surgeons to build breadth of expertise.

What services do Mohs histology consulting firms offer?

Mohs histology consultants offer a range of services to assist practices with establishing or enhancing their frozen section Mohs capabilities:

  • Guidance on optimal Mohs lab set-up, equipment selection, and workflow design
  • Staff training on Mohs techniques, cryostat operation, specimen orientation, and documentation
  • Recruitment assistance for hiring experienced Mohs histology personnel
  • Troubleshooting technical histology issues like frozen sectioning problems
  • Ensuring proper protocols are in place for quality assurance, safety, and accreditation
  • Advice on process improvements, digital pathology implementation, and continuing staff education

Meet with Our Specialists to Evaluate Your Case and Mohs Surgery Options

We hope this detailed overview has provided insight into the highly specialized Mohs surgery process and the vital role of Mohs histology in ensuring successful skin cancer treatment. Our fellowship-trained Mohs surgeons and experienced Mohs histology staff are dedicated to providing the most advanced, effective care for the removal of complex skin cancers. 

If you have been diagnosed with skin cancer, especially in a cosmetically or functionally sensitive area, we encourage you to meet with one of our specialists to discuss if Mohs micrographic surgery is the right treatment option for you.

Schedule a consultation at our website today. Let's work together to develop a customized treatment plan for your skin cancer.

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