A glimpse behind the scenes of uncommon cancers

Tampa Bay, Fla. - Sentinel lymph node biopsy (SLNB) is quickly becoming a routine part of the diagnostic and prognostic toolkit for many cancers, not only for melanoma, but also for some more unusual but equally nasty characters.

"It is amazing how quickly sentinel lymph node biopsy has become part of standard of care in evaluating metastasis of melanoma," says James M. Spencer, M.D., a dermatologist in private practice in the Tampa Bay, Fla., area who specializes in treating skin cancers.

He says the biopsy "provides valuable prognostic information of occult metastasis, but there is poor evidence that it is therapeutically useful," in part because metastasized melanoma does not respond well to therapy.

Accurate prognostic information's chief value seems to be to either set the patient's mind at rest that metastasis has not occurred, or to alert the patient to put his or her affairs in order.

Dr. Spencer believes the procedure has become so popular with physicians because "We want to be helpful," even though the procedure has not been proven to be therapeutically beneficial.

Merkle cell picture

Merkle cell carcinoma (MCC) is uncommon but not rare and initially can be mistaken for basal cell carcinoma, though histology clinches the diagnosis.

Incidence is increasing by 8 percent a year. Perhaps this is because of the aging population and greater use of immunosuppressants; the cancer is associated with a weakened immune state.

The initial intervention is excision of the tumor, generally via Mohs surgery, with ample margins around the tumor. Unlike melanoma, which is resistant to radiation, MCC is sensitive to local irradiation, and many physicians have moved toward using irradiation as an adjunct to surgery. The studies supporting this are small and underpowered, but a meta-analysis suggests a strongly protective effect from relapse by using the adjuvant therapy.

One surprising finding that has emerged is that the size of the MCC tumor at time of diagnosis is not associated with survival.

Argument for SLNB

"Merkel cell carcinoma shares with a deep melanoma the trait of aggressive spread, usually first to the draining lymph nodes," Dr. Spencer tells Dermatology Times.

This fact suggests to him that sentinel lymph node biopsy might be useful both in making a prognosis and in guiding a therapeutic decision on whether to initiate further radiation treatments.

The most complete study of MCC metastasis to date consisted of 61 patients at the Dana-Farber Cancer Institute, 30 of whom later underwent a sentinel lymph node biopsy to evaluate for possible metastasis.

These SLNB specimens showed that "Metastasis was real common," Dr. Spencer notes.

The study found that about a third of MCC patients had occult metastasis, compared with about 5 percent seen with melanoma. The metastasis was not detected through physical examination of the patient. CT scans did not prove to be sensitive enough, although MRI was better. Biopsy was clearly the better tool, though it is not perfect and is subject to variations of sampling and interpretation.

"As with melanoma, the sentinel lymph node biopsy provided useful prognostic information for these patients with metastasized Merkle cell carcinoma," Dr. Spencer says.

But it also directed treatment; 27 patients received additional therapy and remained free from relapse over the course of the study.

However, the still relatively small number of patients with MCC makes it difficult to conduct randomized controlled trials of sufficient power to definitively answer questions as to the best course of therapy for these patients. Practitioners are left with a series of case studies and small studies that can only suggest how best to treat this malignancy.

Another nasty character

Sebaceous gland carcinoma is an even more uncommon form of skin cancer.

"About 80 percent of cases occur around the eyes; about a third metastasize, and they can do so early during the course of disease," Dr. Spencer says.