Adenocarcinomas of the buttock and perianal area are rare, with most the articles published in the literature being case reports. Perianal adenocarcinomas can develop from perianal fistula. Adenocarcinomas related to the fistula tract type almost present mucinous type[1,2]. Mucinous adenocarcinomas of the buttock and perianal area are also reported in hidradenitis suppurativa (HS) or Crohn's disease, which rarely occur[3-5].
The etiology or natural course of the mucinous adenocarcinoma of the buttock is not clearly known because of the rarity of the disease. Its diagnostic criteria were as follows: (1) The fistula should predate the carcinoma; (2) There should be no synchronous colorectal carcinoma; and (3) The internal opening of the fistula should be into the anal canal and not the malignancy. However, it is often difficult to identify the disease origin since these criteria do not appear in all cases[3,7]. Here, we report a case of mucinous adenocarcinoma of the buttock with an atypical diagnostic course.
A 62-year-old man, who complained of recurrent abscesses of the buttock, was referred to the Division of Colon, Rectum and Anus for treatment.
History of present illness
The patient had recurrent abscesses of the buttock for 3 years and had undergone incision and drainage at a local clinic. Although the abscess was resolved with treatment, it recurred. The patient had several abscess sites on the buttock, but no anal discharge, bloody stools, fever, chills, or weight loss were noted. He was otherwise healthy.
History of past illness
He had been taking anti-hypertensive medication and antiplatelet drugs for hypertension for 4 years. However, he had no significant past medical or surgical history. He had no history of anal diseases, such as anal fistulas, hemorrhoids, or perianal abscesses. He had no history of other skin diseases.
His vital signs were normal. He had several scars and nodules on the bilateral buttocks (Figure 1). Purulent discharge drained from one site on the left buttock. Other sites on the left buttock, which showed no drainage, were composed of granulation tissue. Several nodules with skin lesions on the right buttock were observed; however, the discharge was not purulent but serous. There were no lesions in the anus on digital rectal examination. The site of the skin nodule did not originate from the anus through physical examination. He had no symptoms indicative of other diseases. Finally, he was diagnosed with recurrent abscess due to HS at the first visit.
Figure 1 Clinical appearance of buttocks.
The laboratory test included complete blood count, liver function, kidney function, and electrolyte and coagulation profiles, which were within normal limits. Carcinoembryonic antigen and CA19-9 levels were 4.93 ng (normal range, 0-10 ng) and 39.69 U/mL (normal range, 0-37 U/mL), respectively.
He underwent pelvic computed tomography (CT) before the operation because of the prolonged duration of symptoms suggesting the possibility of undiagnosed disease. CT showed an approximately 10 cm in length of abscess in the subcutaneous tissue of the bilateral buttocks (Figure 2A). There was no evidence of its relationship with the anus. After the first operation, he underwent gastroscopy, colonoscopy, transanal ultrasonography (TRUS), and positron emission tomography (PET) to determine the disease origin and condition, as he was diagnosed with mucinous adenocarcinoma. The results of all examinations other than PET were unremarkable. There was no evidence of anal fistula on TRUS. PET showed increased fluorodeoxyglucose uptake in the abscess cavity, buttock, and perianal wall (Figure 2B). It also showed increased fluorodeoxyglucose uptake in the prostate, which suggested inflammation or malignancy. The patient was diagnosed with inflammation of the prostate based on prostate biopsy findings.
Figure 2 Radiologic findings.
A: Computed tomography findings before the first operation show a huge abscess cavity in bilateral buttocks; B: Positron emission tomography findings show 18F-fluorodeoxyglucose uptake along the abscess cavity.
Personal and family history
He had no significant personal or familial history. Moreover, there was no history of cancer in his family.
It is difficult to diagnose mucinous adenocarcinoma of the perineum. They are usually associated with chronic inflammation and manifest as persistent symptoms, regardless of the conventional treatment[8,9]. Most patients present with perianal purulent discharge, a palpable peripheral mass, an ulcer or a recurrent abscess, which are non-specific symptoms regardless of original disease[3,4,9,10]. Patients with a tumor originating from a perianal fistula have a history of a fistula or persistent disease[3,11,12]. Although diagnostic criteria have been developed, the diagnosis of adenocarcinoma from a perianal fistula is difficult as the symptoms are nonspecific. Therefore, mucinous discharge from the anal fistula provides evidence suggestive of carcinoma. T2-weighted magnetic resonance imaging shows a high signal intensity in some cases[3,14,15]. However, many patients are diagnosed on the basis of official or operative biopsy[16,17].
Patients with a tumor originating from HS also have a history of HS and symptoms similar to those of patients with a perianal fistula[4,18]. Patients with a tumor originating from HS present with HS for at least 10 years[19,20]. The tumor originating from HS may be located in the perianal region, perineum, and buttocks[4,20]. The most common tumor type originating from HS is squamous adenocarcinoma, but it could be mucinous adenocarcinoma in some cases, in contrast to the tumor types originating from a perianal fistula[19,20].
Immunochemistry is commonly performed to determine the site of origin of the carcinoma[21,22]. CKs are an epithelial class of intermediate-sized filament proteins in the cytoskeleton. CK7 is present in lung, breast, and female genital tract carcinomas. CK20 is found in the gastrointestinal, urothelium, and Merkel cell carcinomas[23,24]. Adenocarcinomas of the small bowel, appendix, and colorectum express negative CK7 and positive CK20[23-25]. Although a report of a case of mucinous adenocarcinoma from perianal abscesses stated that CK7 and CK20 were immunopositive, the immunochemistry results in this study indicated that the carcinoma had a colorectal origin. Another useful marker is CDX2, which indicates intestinal differentiation. CDX2 is a caudal homeobox gene related to the proliferation and differentiation of intestinal epithelial cells. CDX2 expression presents in at least 85% of overall colorectal adenocarcinomas[26,27]. In this study, the first abscess of the patient developed in the left buttock, and the lesion persisted. The patient had no perianal symptoms. The initial diagnosis made in the outpatient clinic was recurrent HS. However, the immunohistochemistry results showed that the disease originated from the lower gastrointestinal tract. The authors suggested that this mucinous adenocarcinoma might be related to the anal fistulas that healed but remained as an abscess.
The treatment of mucinous adenocarcinomas of the buttock and perianal region depends on the location of the lesion and origin of the disease. Mostly, the surgical treatment is abdominoperineal resection (APR) with or without a wide local excision. Patients with mucinous adenocarcinoma involved with an anal fistula undergo APR, similar to patients with Crohn's anal fistula[5,11]. Even if the disease does not involve the anus, most patients with associated HS undergo APR[4,19]. Patients with wide excision underwent reconstructive operations[12,17,28]. In a case report similar to this one, the patient underwent a local wide resection, and there was no gross evidence of anal canal involvement. The authors also considered APR as a curative treatment; however, the patient refused permanent colostomy, as there was no evidence of fistula. Moreover, many patients with perianal mucinous adenocarcinoma underwent further aggressive therapy, such as chemotherapy with or without radiotherapy[16,29,30]. Neoadjuvant or adjuvant chemoradiotherapy showed better results, although the number of patients was small[16,29,30]. The authors considered performing adjuvant chemoradiotherapy; however, the patient refused further treatment.