Melanocytic Imposters May Masquerade as Melanoma in Situ on Sun-Damaged Skin

SAN DEIGO — An accurate diagnosis of melanoma in situ is often lifesaving, but its histology can be difficult to distinguish from benign histologic findings, Dr. Philip E. LeBoit said at the annual meeting of the California Society of Dermatology and Dermatologic Surgery.

Numerous and prominent melano-cytes on sun-damaged facial skin, particularly those that are near the eyelids, can easily be confused with those seen in melanoma in situ, as can enlarged melanocytes stimulated by a recent excision, said Dr. LeBoit, professor of clinical pathology and dermatology at the University of California, San Francisco.

Dr. Barbara Gilchrest and her associates first highlighted the presence of “actinic melanocytosis” when they reported many years ago that the basal layer of sun-damaged skin in patients of all ages contains twice the expected number of melanocytes (J. Invest. Dermatol. 1979;73:141–3). That finding was recently confirmed and elaborated upon in a recent study by Dr. Ali Hendi and associates.

“So it's not just an increase in the prominence or an increase in the size of melanocytes due to the macules around them in sun-damaged skin. There's actually an increase in number,” Dr. LeBoit said.

If dyschromia or solar lentigos further confuse the picture on facial skin, where there are more melanocytes than on other parts of the body, “nature is confounding you,” he said.

Dr. LeBoit offered the following clues, which he said should heighten the suspicion that a lesion is a melanoma in situ, rather than an artifact of skin that has been damaged by the sun:

▸ The presence of irregular intervals between melanocytes.

▸ Nests, which may be present in melanoma in situ, but not in actinic melanocytosis. Levels may be required to show them.

▸ Pagetoid spread, which also may require levels to be visualized.

▸ Prominent dendrites, which are sometimes, though not necessarily always, present in melanoma in situ. Dr. LeBoit cautioned, however, that dendrites may be seen more prominently in dark-skinned patients.

▸ More irregular pigmentation.

▸ More marked adnexal involvement, except in the case of lentigo melanoma. (In actinic melanocytosis, large melanocytes may extend more deeply or symmetrically in the follicular infundibula and acrosyringia.)

Immunohistochemical studies using HMB-45 or Ki-67(MIB-1) stains are of little use in distinguishing melanoma in situ from actinic melanocytosis, he pointed out.

The results of recent studies from Italy also suggest that the use of immunoperoxidase stains in this context can lead to the “overdiagnosis” of melanoma in situ, said Dr. LeBoit, who founded and codirects the university's dermatopathology service.

A more reliable alternative is to simply biopsy the contralateral side of sun-exposed facial skin, he suggested.

“If you find the exact same picture, then that's just what the patient's face looks like,” he said.

The second dilemma he posed—that is, distinguishing melanoma in situ from recently excised skin—also has a fairly simple solution, as it turns out.

Dr. LeBoit explained that all biopsies stimulate a release of cytokines during the wound-healing process, which in turn activates melanocytes, especially on facial skin.

“Even the best dermatopathologists in the world sometimes cannot tell melanocyte activation by the wound-healing process from the very edge of a melanoma in situ,” he asserted.

His solution? Wait to reexcise.

“Once you've gotten a clinically evident melanoma in situ out, although the patient may be anxious, there is no medical reason to bring them in the next day to do a reexcision,” Dr. LeBoit said.

“You can wait a month. At that point, you will have no enlargement of melanocytes to confuse the picture,” he commented.

SAN DEIGO — An accurate diagnosis of melanoma in situ is often lifesaving, but its histology can be difficult to distinguish from benign histologic findings, Dr. Philip E. LeBoit said at the annual meeting of the California Society of Dermatology and Dermatologic Surgery.

Numerous and prominent melano-cytes on sun-damaged facial skin, particularly those that are near the eyelids, can easily be confused with those seen in melanoma in situ, as can enlarged melanocytes stimulated by a recent excision, said Dr. LeBoit, professor of clinical pathology and dermatology at the University of California, San Francisco.

Dr. Barbara Gilchrest and her associates first highlighted the presence of “actinic melanocytosis” when they reported many years ago that the basal layer of sun-damaged skin in patients of all ages contains twice the expected number of melanocytes (J. Invest. Dermatol. 1979;73:141–3). That finding was recently confirmed and elaborated upon in a recent study by Dr. Ali Hendi and associates.

“So it's not just an increase in the prominence or an increase in the size of melanocytes due to the macules around them in sun-damaged skin. There's actually an increase in number,” Dr. LeBoit said.

If dyschromia or solar lentigos further confuse the picture on facial skin, where there are more melanocytes than on other parts of the body, “nature is confounding you,” he said.

Dr. LeBoit offered the following clues, which he said should heighten the suspicion that a lesion is a melanoma in situ, rather than an artifact of skin that has been damaged by the sun:

▸ The presence of irregular intervals between melanocytes.

▸ Nests, which may be present in melanoma in situ, but not in actinic melanocytosis. Levels may be required to show them.

▸ Pagetoid spread, which also may require levels to be visualized.

▸ Prominent dendrites, which are sometimes, though not necessarily always, present in melanoma in situ. Dr. LeBoit cautioned, however, that dendrites may be seen more prominently in dark-skinned patients.

▸ More irregular pigmentation.

▸ More marked adnexal involvement, except in the case of lentigo melanoma. (In actinic melanocytosis, large melanocytes may extend more deeply or symmetrically in the follicular infundibula and acrosyringia.)

Immunohistochemical studies using HMB-45 or Ki-67(MIB-1) stains are of little use in distinguishing melanoma in situ from actinic melanocytosis, he pointed out.

The results of recent studies from Italy also suggest that the use of immunoperoxidase stains in this context can lead to the “overdiagnosis” of melanoma in situ, said Dr. LeBoit, who founded and codirects the university's dermatopathology service.

A more reliable alternative is to simply biopsy the contralateral side of sun-exposed facial skin, he suggested.

“If you find the exact same picture, then that's just what the patient's face looks like,” he said.

The second dilemma he posed—that is, distinguishing melanoma in situ from recently excised skin—also has a fairly simple solution, as it turns out.

Dr. LeBoit explained that all biopsies stimulate a release of cytokines during the wound-healing process, which in turn activates melanocytes, especially on facial skin.

“Even the best dermatopathologists in the world sometimes cannot tell melanocyte activation by the wound-healing process from the very edge of a melanoma in situ,” he asserted.

His solution? Wait to reexcise.

“Once you've gotten a clinically evident melanoma in situ out, although the patient may be anxious, there is no medical reason to bring them in the next day to do a reexcision,” Dr. LeBoit said.

“You can wait a month. At that point, you will have no enlargement of melanocytes to confuse the picture,” he commented.

SAN DEIGO — An accurate diagnosis of melanoma in situ is often lifesaving, but its histology can be difficult to distinguish from benign histologic findings, Dr. Philip E. LeBoit said at the annual meeting of the California Society of Dermatology and Dermatologic Surgery.

Numerous and prominent melano-cytes on sun-damaged facial skin, particularly those that are near the eyelids, can easily be confused with those seen in melanoma in situ, as can enlarged melanocytes stimulated by a recent excision, said Dr. LeBoit, professor of clinical pathology and dermatology at the University of California, San Francisco.

Dr. Barbara Gilchrest and her associates first highlighted the presence of “actinic melanocytosis” when they reported many years ago that the basal layer of sun-damaged skin in patients of all ages contains twice the expected number of melanocytes (J. Invest. Dermatol. 1979;73:141–3). That finding was recently confirmed and elaborated upon in a recent study by Dr. Ali Hendi and associates.

“So it's not just an increase in the prominence or an increase in the size of melanocytes due to the macules around them in sun-damaged skin. There's actually an increase in number,” Dr. LeBoit said.

If dyschromia or solar lentigos further confuse the picture on facial skin, where there are more melanocytes than on other parts of the body, “nature is confounding you,” he said.

Dr. LeBoit offered the following clues, which he said should heighten the suspicion that a lesion is a melanoma in situ, rather than an artifact of skin that has been damaged by the sun:

▸ The presence of irregular intervals between melanocytes.

▸ Nests, which may be present in melanoma in situ, but not in actinic melanocytosis. Levels may be required to show them.

▸ Pagetoid spread, which also may require levels to be visualized.

▸ Prominent dendrites, which are sometimes, though not necessarily always, present in melanoma in situ. Dr. LeBoit cautioned, however, that dendrites may be seen more prominently in dark-skinned patients.

▸ More irregular pigmentation.

▸ More marked adnexal involvement, except in the case of lentigo melanoma. (In actinic melanocytosis, large melanocytes may extend more deeply or symmetrically in the follicular infundibula and acrosyringia.)

Immunohistochemical studies using HMB-45 or Ki-67(MIB-1) stains are of little use in distinguishing melanoma in situ from actinic melanocytosis, he pointed out.

The results of recent studies from Italy also suggest that the use of immunoperoxidase stains in this context can lead to the “overdiagnosis” of melanoma in situ, said Dr. LeBoit, who founded and codirects the university's dermatopathology service.

A more reliable alternative is to simply biopsy the contralateral side of sun-exposed facial skin, he suggested.

“If you find the exact same picture, then that's just what the patient's face looks like,” he said.

The second dilemma he posed—that is, distinguishing melanoma in situ from recently excised skin—also has a fairly simple solution, as it turns out.

Dr. LeBoit explained that all biopsies stimulate a release of cytokines during the wound-healing process, which in turn activates melanocytes, especially on facial skin.

“Even the best dermatopathologists in the world sometimes cannot tell melanocyte activation by the wound-healing process from the very edge of a melanoma in situ,” he asserted.

His solution? Wait to reexcise.

“Once you've gotten a clinically evident melanoma in situ out, although the patient may be anxious, there is no medical reason to bring them in the next day to do a reexcision,” Dr. LeBoit said.

“You can wait a month. At that point, you will have no enlargement of melanocytes to confuse the picture,” he commented.