Fig. 7.1
Immunohistochemical stains for melanocytes during Mohs surgery. (a) Hematoxylin and eosin-stained frozen section of melanoma in situ (magnification, 20×) with a large nest of melanocytes (blue arrow). The hyperchromatic dark blue nuclei of pagetoid melanocytes (blue triangle) are challenging to discern. (b) MART-1 frozen section immunostain of the same specimen (magnification, 20×). The nest of melanocytes is clearly visible (blue arrow) as well as many more pagetoid melanocytes (blue triangle)
MART-1 staining has some disadvantages. Prominent staining of the cytoplasm in the dendrites of melanocytes may lead to false positive interpretation of MART-1 immunostains, and some authors prefer the crisp nuclear staining pattern with microphthalmia transcription factor (MITF) [30, 31]. MART-1 does not stain pure desmoplastic melanoma, therefore supplemental staining with S-100 or SOX-10 may be necessary [32]. Even after interpretation of margins with high quality immunostains, evaluation of hematoxylin and eosin stains is still necessary to assess keratinocyte atypia, assess cytology of melanocytes, identify desmoplastic melanoma, and evaluate incidental lesions, such as nevi and keratinocytic cancers.
Highly Skilled Mohs Lab Necessary for Melanoma
In the year 2000, only 12 % (13/108) of laboratories run by members of the American College of Mohs Surgery reported the use of frozen section immunostains, possibly due to cost, added time, and lack of training [33]. The current percentage of Mohs laboratories using immunohistochemistry is uncertain. Production and interpretation of high quality melanocytic immunostains requires expertise from both the histotechnologist and the Mohs surgeon. In order to produce 2–4 μm thick tissue sections without artifact or distortion, histotechnicians require excellent training, abundant experience, and high quality equipment [28]. Mohs surgeons must gain adequate training to interpret the margins of melanoma. The Mohs laboratory must have careful protocols in place for quality control, and the Mohs surgeon must be prepared to invest the time and resources necessary to treat melanoma patients.
Local Recurrence After Mohs Surgery
MMS allows for clear microscopic margins with 100 % microscopic evaluation of the peripheral and deep margin, allowing for immediate detection and removal of microscopic melanoma that is not clinically visible. Evidence also demonstrates that partial margin assessment with conventional breadloafed pathology sections increases the risk for false negative margins and local recurrence (Fig. 7.2). By examining the entire surgical margin under the microscope, MMS eliminates the potential for sampling error and decreases local recurrence rates. The low local recurrence rates support the effectiveness of MMS supplemented by immunostains to achieve clear microscopic margins [3, 8, 15–19, 34–36]. However, interpretation of these studies must be taken in context of the variable follow up times and heterogeneous cohorts (Table 7.1).
Fig. 7.2
Local recurrence after incomplete excision. Patient with local recurrence of melanoma after conventional wide local excision with purportedly “clear” microscopic margins and repair with a full-thickness skin graft; melanoma recurred along the margins of the graft
Table 7.1
Melanoma local recurrence rates after Mohs surgery
Mohs without immunostains | ||
|---|---|---|
Reference | Local recurrence rate (%) | Followup mean months {Range} |
Walling et al. [34] | 33 (6/18) | 117.5 {61–157} |
Hou et al. [35] | 1.9 (3/154) | 94.8 |
Zitelli et al. [3] | 0.5 (3/553) | 60 |
Bienert et al. [8] | 0 (0/92) | 33 {8–72} |
Temple and Arlette [36] | 0 (0/202) | 29.8 {0.25–114.6} |
Mohs with immunostains | ||
Newman et al. [18] | 1.1 (5/460) | 34 |
Bhardwaj et al. [19] | 0.5 (1/200) | 38.4 {6–58} |
Bricca et al. [15] | 0.3 (1/331) | 58 {0–238.8} |
Kunishige et al. [16] | 0.3 (3/1120) | 56.4 {0.24–282} |
Etzkorn et al. [17] | 0.3 (2/597) | 33.6 |
Zalla et al. [10] | 0 (0/68) | 16 {1–32} |
Indications for MMS
LMM with subclinical spread benefits from MMS to detect and remove microscopic tumor not visible by clinical examination. Melanomas that require reconstruction with a flap or a graft also benefit from MMS or other margin-controlled techniques to confirm clear microscopic margins prior to reconstruction. A consensus panel representing the American Academy of Dermatology, the American College of Mohs Surgery, the American Society for Dermatologic Surgery, and the American Society for Mohs Surgery deemed MMS to be appropriate for the following clinical scenarios: (1) primary lentigo maligna (LM) and MIS, non-LM type, located on the head and neck, acral sites, genitalia, and pretibial leg; (2) locally recurrent LM and MIS, non-LM type, in any anatomic location [37] (Table 7.2). Although consensus guidelines do not yet include invasive melanoma, the likelihood for subclinical spread and reconstruction with a flap or graft does not differ between melanoma in situ and invasive melanoma. Compared to melanomas on the trunk and proximal extremities, melanomas located on the head and neck, genitalia and distal extremities are nearly twice as likely to have subclinical spread and 10 times more likely to require reconstruction with a flap or a graft. Compared to primary melanomas, locally recurrent melanomas are nearly twice as likely to have subclinical spread or to require reconstruction with a flap or graft [38].
Table 7.2
Indications for Mohs micrographic surgery of melanoma
Tumor location on head and neck, distal extremities, or anogenital area |
|---|
Clinical margins are indistinct as tumor arises in aged or heavily sun-damaged skin |
Large tumor size |
Requirement for reconstruction with a tissue-rearranging flap or large graft |
Tumor has recurred after previous treatment with either excision or destruction |
Advantages of Mohs Surgery
Optimal surgery for melanoma includes three conditions: (1) accurate staging of the primary melanoma prior to reconstruction; (2) excision with clear microscopic surgical margins; and, (3) reconstruction in tumor-free skin. Conventional wide excisional surgery with breadloaf sectioning is not able to meet these conditions for certain melanoma subtypes, especially LMM on the face. To appreciate the relative advantages of MMS for melanoma, one must first understand the different methods of specimen processing and margin evaluation. Table 7.3 summarizes key differences between conventional wide local excision, staged excision techniques with formalin-fixed paraffin-embedded sections, and MMS.
Table 7.3
Comparison of melanoma excision and specimen processing and margin evaluation techniques
Conventional wide local excision | Staged excision variations with paraffin sections | Mohs micrographic surgery | |
|---|---|---|---|
Who excises the tumor? | Surgeon | Surgeon | Mohs surgeon |
Who examines the margin under the microscope? | Dermatopathologist | Dermatopathologist | Mohs surgeon |
How is tissue processed? | Formalin-fixed paraffin-embedded sections | Formalin-fixed paraffin-embedded sections | Frozen tissue sections |
Typical delay between excision and microscopic margin evaluation | 2–5 days | 1–3 days | 1–2 h |
Percentage of surgical margin examined under the microscopic | <1 % (insert reference) | Up to 100 %, depending on method | 100 % |
Ability to perform same day microscopic margin assessment and reconstruction | No | No | Yes |
Detecting Melanoma Upstaging Prior to Reconstruction
Since complete sampling of many LMM is not always practical prior to MMS, the Mohs surgeon may detect upstaging of melanoma prior to reconstruction. MMS combines breadloaf sectioning of the tumor debulking with excision and complete microscopic margin evaluation and mapping [17]. If a patient subsequently upstages to candidacy for sentinel lymph node biopsy (SLNB), the Mohs surgeon may delay reconstruction to maximize the likelihood of an accurate SLNB as shown in Fig. 7.3.
Fig. 7.3
Melanoma upstaging and sentinel lymph node biopsy prior to reconstruction. (a) 49 year old male with melanoma (partial biopsy showed melanoma 0.22 mm, no mitoses, no ulceration) of the right nasal sidewall. The outer circle on the nasal sidewall shows the 7 mm margin excised with the first stage of Mohs surgery (Biopsies marked of an incidental squamous cell carcinoma in situ of the right ala and a melanoma in situ of the right premaxillary cheek). (b) Defect after obtaining clear margins with Mohs surgery. Frozen section breadloaf sections of the debulking excision revealed melanoma invasive to a depth of 0.95 mm. Reconstruction was delayed for sentinel lymph node biopsy. (c) Bandage on preauricular cheek covers incision from sentinel lymph node biopsy. Two lymph nodes from the left parotid gland showed no evidence of metastasis. (d) After sentinel lymph node biopsy, patient returned for reconstruction under local anesthesia with a paramedian forehead flap. (e) Normal appearance was restored
Breslow depth of melanoma may be measured using frozen section examination [39]. In a cohort of 614 patients treated with MMS that combined breadloaf frozen sectioning of the central debulking excision with complete peripheral and deep microscopic margin evaluation, 1.3 % (8/614) of the melanomas upstaged to candidacy for SLNB after evaluation of the breadloafed debulking specimen [17]. In 7 of 8 of these cases, a discussion about SLNB ensued prior to reconstruction, and the patient elected to delay reconstruction and undergo SLNB in three cases. While the role of SLNB for melanoma remains controversial, especially after an excision, it is recommended for staging of patients with melanomas of T1b or greater [40] as illustrated in Fig. 7.4. Although further study is needed, SLNB is considered more accurate prior to tissue rearrangement from reconstructive surgery.
Fig. 7.4
Partially biopsied melanoma with unsuspected invasion and melanoma upstaging. (a) Partially biopsied melanoma (Breslow depth 0.65 mm, 2 mitosec/mm2, no ulceration); patient declined sentinel lymph node biopsy. (b) Mohs micrographic surgery with 1 cm margin cleared margins. Tumor debulking revealed focal unsuspected invasion to a Breslow depth of 2.3 mm; upstaged from stage IB to IIA (T3aN0M0). (c) Sentinel lymph node biopsy offered prior to reconstruction of defect
Mohs Excision with Clear Histologic Margins Prior to Reconstrution
Just as partial biopsies of melanoma may yield unreliable tumor staging, partial sampling of surgical margins may result in false negative microscopic margins [41]. The method of tissue processing determines the amount of the surgical margin available for microscopic assessment [42]. Breadloaf sectioning, which remains the most common method to process tissue after conventional excision of melanoma, typically examines <1 % of the microscopic surgical margin. The risk for false negative margins increases as the number of breadloaf sections decreases [43]. Local recurrence rates remain high for subsets of melanoma such as LMM, even after excision with purportedly clear margins. For example, approximately 10 % (range 2.8–28 %) of melanomas on the head and neck recur locally after conventional excision of melanomas on the head and neck [17]. Figure 7.5 illustrates a LMM with indistinct clinical margins with persistent melanoma at surgical margins after 7 prior conventional excisions.
