9 tips to help prevent derm biopsy mistakes

An advantage of the punch biopsy is that patients are left with linear scars rather than round, potentially dyspigmented (darker or lighter) scars that are often associated with shave biopsy. A well-sutured punch biopsy can be cosmetically elegant, particularly if closure is oriented along relaxed skin tension lines. For this reason, punch biopsies are well suited for cosmetically sensitive locations such as the face, although shave biopsies are also often performed on the face.

4. Choose an excisional biopsy for a melanocytic neoplasm, when possible.

The purpose of an excisional biopsy (which typically includes a 1 to 3 mm rim of normal skin around the lesion) is to completely remove a lesion. The excisional biopsy generally is the preferred technique for clinically atypical melanocytic neoplasms (lesions that are not definitively benign).^4-8

When suspicion for melanoma is high, excisional biopsies should be performed with minimal undermining to preserve the accuracy of any future sentinel lymph node biopsy surgeries. Excisional biopsy is the most involved type of biopsy and has the largest potential for cosmetic disfigurement if not properly planned and performed. While guidelines from the American Academy of Dermatology state that “narrow excisional biopsy that encompasses [the] entire breadth of lesion with clinically negative margins to ensure that the lesion is not transected” is preferred, they also acknowledge that partial sampling (incisional biopsy) is acceptable in select clinical circumstances,⁹ such as when a lesion is large or on a cosmetically sensitive site such as the face.¹⁰

While a larger punch biopsy (6 or 8 mm) or even deep shave/saucerization may function as an excisional biopsy for very small lesions, this approach can be problematic. For one thing, these biopsies are more likely than an excisional biopsy to leave a portion of the lesion in situ. Another concern is that a shave biopsy of a melanocytic lesion can lead to error or difficulty in obtaining the correct diagnosis on later biopsy.¹¹ For pathologists, smaller or incomplete samples make it challenging to establish an accurate diagnosis.¹² Among melanomas seen at a tertiary referral center, histopathological misdiagnosis was more common with a punch or shave biopsy than with an excisional biopsy.⁹

It has been shown that partial biopsy for melanoma results in more residual disease at wide local excision and makes it more challenging to properly stage the lesion.^13,14 If a shave biopsy is used to sample a suspected melanocytic neoplasm, it is imperative to document the specific site of the biopsy, indicate the size of the melanocytic lesion on the pathology requisition form, and ensure that all (or nearly all) of the clinically evident lesion is sampled. Detailing the location of the lesion in the chart is not only essential in evaluating the present lesion, but it will serve you well in the future. Without knowing the patient’s clinical history, benign nevi that recur after a prior biopsy can be difficult to histologically distinguish from melanoma (FIGURE 3). For more on this, see tip #7.

5. Be careful with curettage.

6. Remember the importance of proper fixation and processing.

As obvious as it may sound, it is important to remember to promptly place sampled tissue in an adequate amount of formalin so that the tissue is submersed in it in the container.¹⁵ Failure to do so can result in improper fixation and will make it difficult to render an appropriate diagnosis. Conventionally, a 10:1 formalin volume to tissue volume ratio is recommended. If the “cold time”—the amount of time a tissue sample is out of formalin—is long enough (greater than a few hours), an appropriate assessment can be impossible.

Appropriate fixation and fixation times are important because molecular testing is being increasingly used to make pathological diagnoses.¹⁶ Additionally, aggressively manipulating a biopsy sample while extracting it or placing it in formalin can cause “crush” artifact, which can limit interpretability (FIGURE 5).

7. Properly photograph and document the biopsy location.

When performing a biopsy of a suspicious neoplasm, physicians often remove all of the lesion’s superficial components, which means that at the patient’s follow-up appointment and subsequent treatments, only a well-healed biopsy site will remain. The biopsy site may be so well healed that it blends seamlessly into the surrounding skin and is nearly impossible for the physician to identify. This problem is seen most often when patients present for surgical excision or Mohs micrographic surgery.¹⁷