Comments on “Eccrine Porocarcinoma: A Multicenter Retrospective Study with Review of the Literatures Reported in Korea”

Dear Editor:

Kim et al.1 recently published an article on eccrine porocarcinoma (EPC) titled, “Eccrine porocarcinoma: A multicenter retrospective study with review of the literatures reported in Korea,” which we read with great interest. We appreciate the effort of gathering all prior relevant Korean cases and thoroughly reviewing the clinical and histological features of the cases from their institutions. Unlike previous reports2, the most common site of EPC among 37 cases in Kim et al.1 was the head and neck region (11 cases), followed by the trunk (10 cases) and lower extremities (9 cases). However, according to our institute’s 20-year data (January 2000 to December 2019), among 10 histologically proven EPC cases, 6 occurred in the lower extremities, while 3 occurred in the head and neck region. As two cases had been reported in the literature3, we report additional 8 cases. Of the 45 EPC cases reported in Korea, 14 (31.1%) occurred in the lower extremities and another 14 (31.1%) occurred in the head and neck region. More cases are needed to suggest that EPC most commonly occurs in the head and neck region in Korea.

We compared the Korean data of 45 patients with data from the US National Cancer Database4. In the Korean and US cases, no sexual predisposition was observed. No significant differences in the primary site and lesion size were found (Table 1).

Table 1
Comparison between US and Korean eccrine porocarcinoma data

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To update the data on EPC cases in Korea, we are reporting the clinical features of the 10 cases from our institute. The clinical characteristics of the 10 patients are summarized in Table 2.

Table 2
Clinical characteristics of ten patients with eccrine porocarcinoma from our institution

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Of note, 5 (50%) of our cases had eccrine poroma as the associated benign component. When adding to the predisclosed data of the 37 patients in Kim et al.’s article1, among the 45 patients in Korea, 15 (33.3%) had preexisting poromas. Dermatologists should be aware of the considerable potency of eccrine poroma to evolve into a malignancy.

Kim et al.1 stated that although most metastases of EPC in Korean patients were found at diagnosis, metastases were spotted months later in 2 cases. In our cases, one patient had no metastases on initial imaging. However, 1 year after wide excision with clear margins, the lesion metastasized to the regional lymph node (right inguinal). Three years after the excision, the tumor metastasized to distant lymph nodes (left supraclavicular and axillary) and the bone (T4–L1 vertebral body). Although guidelines for imaging are lacking, we believe that imaging studies during follow-up may be useful for the detection of metastases.

Recently, van den Brand et al.5 reported a case of EPC in situ with lymph node metastases that led to the death of the patient. Considering that even in situ lesions may metastasize, we believe imaging at diagnosis may also be beneficial.

In conclusion, more data are needed to explore the most common site of EPC in Korea. For eccrine poroma lesions, we suggest complete excision before malignant transformation and for patients with EPC, we recommend imaging studies to detect metastases initially and during follow-up.