ISSN: 2754-8880
Published 00 11 0000
OPEN ACCESS
Edited by
A.Hussain
Submitted 28 Nov. 2025
Accepted 21 Dec. 2025
Citation
N Tilawatu,M Fahmi,M Abd
Rahman,A Faidzal.Mucinous
Adenocarcinoma Arising
From Chronic Fistula-In-
Ano: A Case Report, Editorial
article:BJOSS::2026:(6);175-
178
Mucinous Adenocarcinoma Arising From
Chronic Fistula-In-Ano: A Case Report
N Tilawatu1*, M Fahmi1, M Abd Rahman1, and A Faidzal1
1Department of Surgery, Sultan Ahmad Shah Medical Centre @IIUM, Jalan Sultan Haji Ahmad
Shah, Bandar Indera Mahkota, 25200 Kuantan, Pahang, Malaysia.
*Corresponding author: Noor Tilawatu Kamaruddin. Department of Surgery, Sultan Ahmad
Shah Medical Centre @IIUM, Jalan Sultan Haji Ahmad Shah, Bandar Indera Mahkota, 25200
Kuantan, Pahang, Malaysia E-mail address: noor_tilawatu@yahoo.com. ORCID iD :
0009-0003-8429-6055
ORIGINAL
Abstract
Mucinous adenocarcinoma of the fistula tract is a rare consequence of fistula-in-ano accounted
for approximately 2-3% of perianal cancers. Due to its rarity, no specific guidelines are available
on diagnostic modality and treatment of choice. Early diagnosis carries a good prognosis, but
most of the time, patients are presented with advanced stages of disease. Chronic and recurrent
perianal fistula and abscess often mask the malignant transformation, especially when the index
of suspicion is low. Diagnosis is ascertained by tissue biopsy and supported by imaging modality
such as MRI. Oncological resection with neoadjuvant or adjuvant radiotherapy and systemic
therapy is proven to have a benefit in a patient’s overall survival. This article reports a case of
mucinous adenocarcinoma of the fistula tract in a 61-year-old gentleman who had a previous
history of recurrent unresolved perianal sepsis and fistula.
Keywords: perianal fistula, anorectal adenocarcinoma, fistula-in-ano
Introduction
Complex fistula-in-ano (FIA) is a common surgical condition in anorectal surgery; the cases of
malignant transformation are rare. Complex FIA are commonly due to Crohn’s disease, radiation
treatment, and recurrent infection (1). The pathophysiology of carcinoma transformation from
chronic FIA is possible due to chronic inflammation with recurrent epithelial regeneration (2).
Early diagnosis is challenging as the symptoms often mimic recurrent benign conditions with
tissue biopsy usually fails to obtain infiltrating malignant tissue. Late diagnosis of the condition led
to a delay in treatment and a poor prognosis in advanced disease, which proved a good prognosis
in aggressive surgical and neoadjuvant or adjuvant chemoradiation therapy. This case highlights a
gentleman with recurrent FIA diagnosed with malignant transformation of complex FIA.
Case presentation
A 61-year-old man presented with recurrent perianal discharge and buttock swelling for 5 years.
He had multiple visits to various centres and was treated as a complex FIA. He underwent
multiple surgeries over a period of 5 years. However, the FIA kept recurring and complicated
with abscess (Figure 1). A computed tomography (CT) of the pelvis and CT-guided percutaneous
drainage for recurrent perianal abscess were performed. Subsequent magnetic resonance imaging
(MRI) revealed circumferential low rectal wall thickening with a fistulous tract and multiloculated
collection with associated pelvic and inguinal lymphadenopathy as well as an extensive bony
lesion. Colonoscopy showed proctitis, and the histological assessment revealed inflammatory
lesions. Repeated biopsy from a wedged biopsy reported as adenocarcinoma with mucinous
differentiation. He was planned for neoadjuvant chemotherapy followed by abdominoperineal
resection (APR). However, the patient’s condition was further deteriorating, and he passed away
before initiating the treatment.
Figure 1. Physical examination showed bilateral gluteal swelling with multiple fistula tract with
growth.
Figure 2. Axial and sagittal view magnetic resonance imaging of pelvis showed circumferential
low rectal wall thickening with multiloculated collection and pelvis lymphadenopathy.
Discussion
In coloproctology, anal fistula is a common benign disease; however, perianal adenocarcinoma
associated with chronic FIA is an extremely rare occurrence, making up to 6.9% of all cancers
in the anal canal ( 3). Meanwhile, mucinous adenocarcinoma accounted for approximately 2-3%
of perianal cancers. Inflammatory bowel disease and Lynch syndrome are the most frequent
causes of mucinous adenocarcinoma, and patients with radiation-induced colorectal cancers have
a higher incidence of this condition. There have been a few cases where chronic FIA has been
linked to mucinous adenocarcinoma. The pathophysiology of malignant transformation remains
176/178
differentiation. He was planned for neoadjuvant chemotherapy followed by abdominoperineal
resection (APR). However, the patient’s condition was further deteriorating, and he passed away
before initiating the treatment.
Figure 1. Physical examination showed bilateral gluteal swelling with multiple fistula tract with
growth.
Figure 2. Axial and sagittal view magnetic resonance imaging of pelvis showed circumferential
low rectal wall thickening with multiloculated collection and pelvis lymphadenopathy.
Discussion
In coloproctology, anal fistula is a common benign disease; however, perianal adenocarcinoma
associated with chronic FIA is an extremely rare occurrence, making up to 6.9% of all cancers
in the anal canal ( 3). Meanwhile, mucinous adenocarcinoma accounted for approximately 2-3%
of perianal cancers. Inflammatory bowel disease and Lynch syndrome are the most frequent
causes of mucinous adenocarcinoma, and patients with radiation-induced colorectal cancers have
a higher incidence of this condition. There have been a few cases where chronic FIA has been
linked to mucinous adenocarcinoma. The pathophysiology of malignant transformation remains
176/178
unclear, but persistent inflammation accompanied by frequent epithelial regeneration has been
implicated (2).
Clinical presentation often revealed symptoms of perianal pain, swelling, and discharge, and
examination showed multiple fistula tracts with abscesses. A complete examination must include
digital rectal examination and anoscope, which is usually conducted under anaesthesia due to
discomfort and pain (1). A case series reported by McIntyre JM in 1948 concluded that one should
consider the possibility of carcinoma in the anal fistula when the fistula has been present for many
years, the fistula becomes more painful or indurated and the drainage becomes more mucinous in
character (4). Definite diagnosis is based on biopsy and histopathology report, although obtaining
adequate and right tissue for biopsy is challenging because the mucinous component of the tumor
is much larger than the carcinomatous component, which is comparatively small ( 5). Imaging
studies like MRI and CT scans will provide adequate information regarding the invasion of the
disease into the adjacent tissue. MRI is the most sensitive modality (>90%) for diagnosing the
condition. A notable hyper-intense signal can be seen on T2-weighted images, making pelvic MRI
a valuable imaging modality in this case (6). However, a combination of two imaging modalities,
such as MRI, endoanal ultrasound, fistulography, and CT scan are proven to provide diagnostic
accuracy up to 100% (1).
The standard treatment is oncological resection. The most recommended surgical technique
is APR; in more complex cases, securing a negative resection margin requires extensive exci-
sion of surrounding tissues, including the overlying skin. Neoadjuvant or adjuvant therapy like
chemotherapy, radiotherapy, or chemoradiotherapy can be considered; however, the efficacy
is still debatable. A study conducted by Gaertner et al, 8 out of 14 patients with anal fistula
malignancy showed no evidence of disease after neoadjuvant or adjuvant therapy with APR ( 7 ).
In other reported cases by Inoue et al in Japan, 3 out of 9 patients who underwent combination
treatment have shown a good response. A total of 2 of the patients had local recurrence during
follow up at 56 months despite receiving CCRT and APR with a good margin (8 ). Diaz-Vico et al
reported 3 cases of mucinous adenocarcinoma arising from chronic perianal fistula from their
centre; all 3 cases received neoadjuvant CRT and primary surgery, 2 of them received adjuvant
oral chemotherapy, which showed good response and no recurrence; however, another 1 did not
receive postoperative chemotherapy due to a medical condition and developed nodal metastasis
at 26-month follow-up (9).
Distant metastases are uncommon in mucinous adenocarcinoma, and tumor spread is typically
lymphatic, with inguinal nodes being the most common location of metastases as seen in our case
( 10). Higher suspicion of malignancy should be aroused in view of a long-standing chronic fistula
and recurrent abscess. Prognosis is worse in mucinous adenocarcinoma when the tumor is larger
than 5cm (>T3), or nodal or hematogenous metastases are present at times of diagnosis (7; 8).
Conclusion
A malignant transformation of complex FIA, although rare, should be considered in patients with
long-standing, recurrent perianal fistulas, especially when clinical features such as persistent
pain, induration, and mucinous discharge are present. Accurate diagnosis requires a combination
of imaging and repeated histopathological assessment, as initial biopsies may fail to detect
malignancy due to the tumor’s mucinous nature. Early detection and aggressive treatment with
oncological resection and appropriate chemoradiotherapy offer the best chance for improved
outcomes, although the overall prognosis remains guarded in advanced cases.
Conflict of Interest
All authors declare no conflict interest of any kind.
177/178
implicated (2).
Clinical presentation often revealed symptoms of perianal pain, swelling, and discharge, and
examination showed multiple fistula tracts with abscesses. A complete examination must include
digital rectal examination and anoscope, which is usually conducted under anaesthesia due to
discomfort and pain (1). A case series reported by McIntyre JM in 1948 concluded that one should
consider the possibility of carcinoma in the anal fistula when the fistula has been present for many
years, the fistula becomes more painful or indurated and the drainage becomes more mucinous in
character (4). Definite diagnosis is based on biopsy and histopathology report, although obtaining
adequate and right tissue for biopsy is challenging because the mucinous component of the tumor
is much larger than the carcinomatous component, which is comparatively small ( 5). Imaging
studies like MRI and CT scans will provide adequate information regarding the invasion of the
disease into the adjacent tissue. MRI is the most sensitive modality (>90%) for diagnosing the
condition. A notable hyper-intense signal can be seen on T2-weighted images, making pelvic MRI
a valuable imaging modality in this case (6). However, a combination of two imaging modalities,
such as MRI, endoanal ultrasound, fistulography, and CT scan are proven to provide diagnostic
accuracy up to 100% (1).
The standard treatment is oncological resection. The most recommended surgical technique
is APR; in more complex cases, securing a negative resection margin requires extensive exci-
sion of surrounding tissues, including the overlying skin. Neoadjuvant or adjuvant therapy like
chemotherapy, radiotherapy, or chemoradiotherapy can be considered; however, the efficacy
is still debatable. A study conducted by Gaertner et al, 8 out of 14 patients with anal fistula
malignancy showed no evidence of disease after neoadjuvant or adjuvant therapy with APR ( 7 ).
In other reported cases by Inoue et al in Japan, 3 out of 9 patients who underwent combination
treatment have shown a good response. A total of 2 of the patients had local recurrence during
follow up at 56 months despite receiving CCRT and APR with a good margin (8 ). Diaz-Vico et al
reported 3 cases of mucinous adenocarcinoma arising from chronic perianal fistula from their
centre; all 3 cases received neoadjuvant CRT and primary surgery, 2 of them received adjuvant
oral chemotherapy, which showed good response and no recurrence; however, another 1 did not
receive postoperative chemotherapy due to a medical condition and developed nodal metastasis
at 26-month follow-up (9).
Distant metastases are uncommon in mucinous adenocarcinoma, and tumor spread is typically
lymphatic, with inguinal nodes being the most common location of metastases as seen in our case
( 10). Higher suspicion of malignancy should be aroused in view of a long-standing chronic fistula
and recurrent abscess. Prognosis is worse in mucinous adenocarcinoma when the tumor is larger
than 5cm (>T3), or nodal or hematogenous metastases are present at times of diagnosis (7; 8).
Conclusion
A malignant transformation of complex FIA, although rare, should be considered in patients with
long-standing, recurrent perianal fistulas, especially when clinical features such as persistent
pain, induration, and mucinous discharge are present. Accurate diagnosis requires a combination
of imaging and repeated histopathological assessment, as initial biopsies may fail to detect
malignancy due to the tumor’s mucinous nature. Early detection and aggressive treatment with
oncological resection and appropriate chemoradiotherapy offer the best chance for improved
outcomes, although the overall prognosis remains guarded in advanced cases.
Conflict of Interest
All authors declare no conflict interest of any kind.
177/178
References
[1] Kim HC, Simianu VV. Contemporary management of anorectal fistula. Surgical Open Science.
2024;17:40-3.
[2] Tahir M, Rahman J, Zubair T, et al. An association of mucinous adenocarcinoma with chronic
peri-anal fistula: A brief review of pathophysiology of rare tumor. Cureus. 2020;12(6):e8882.
[3] Khalafi S, Riddle M, Harper B, et al. Perianal mucinous adenocarcinoma found incidentally
from perianal mass. Cureus. 2023;15(11):e48314.
[4] McIntyre JM. Carcinoma associated with fistula-in-ano. American Journal of Surgery.
1952;84(5):610-3.
[5] Okada K, Shatari T, Sasaki T, et al. Is histopathological evidence really essential for making a
surgical decision about mucinous carcinoma arising in a perianal fistula? Report of a case.
Surgery Today. 2008;38(6):555-8.
[6] Oberholzer K, Menig M, Kreft A, et al. Rectal cancer: mucinous carcinoma on magnetic
resonance imaging indicates poor response to neoadjuvant chemoradiation. International
Journal of Radiation Oncology, Biology, Physics. 2012;82(2):842-8.
[7] Gaertner WB, Hagerman GF, Finne CO, et al. Fistula-associated anal adenocarcinoma: good
results with aggressive therapy. Diseases of the Colon & Rectum. 2008;51(7):1061-7.
[8] Inoue Y, Kawamoto A, Okigami M, Okugawa Y, Hiro J, Toiyama Y, et al. Multimodal-
ity therapy in fistula-associated perianal mucinous adenocarcinoma. American Surgeon.
2013;79(9):e286-8.
[9] Díaz-Vico T, Fernández-Martínez D, García-Gutiérrez C, Suárez J, et al. Mucinous adeno-
carcinoma arising from chronic perianal fistula: a multidisciplinary approach. Journal of
Gastrointestinal Oncology. 2019;10(3):589-96.
[10] Santos MD, Nogueira C, Lopes C. Mucinous adenocarcinoma arising in chronic perianal
fistula: good results with neoadjuvant chemoradiotherapy followed by surgery. Case Reports
in Surgery. 2014;2014:386150.
178/178
[1] Kim HC, Simianu VV. Contemporary management of anorectal fistula. Surgical Open Science.
2024;17:40-3.
[2] Tahir M, Rahman J, Zubair T, et al. An association of mucinous adenocarcinoma with chronic
peri-anal fistula: A brief review of pathophysiology of rare tumor. Cureus. 2020;12(6):e8882.
[3] Khalafi S, Riddle M, Harper B, et al. Perianal mucinous adenocarcinoma found incidentally
from perianal mass. Cureus. 2023;15(11):e48314.
[4] McIntyre JM. Carcinoma associated with fistula-in-ano. American Journal of Surgery.
1952;84(5):610-3.
[5] Okada K, Shatari T, Sasaki T, et al. Is histopathological evidence really essential for making a
surgical decision about mucinous carcinoma arising in a perianal fistula? Report of a case.
Surgery Today. 2008;38(6):555-8.
[6] Oberholzer K, Menig M, Kreft A, et al. Rectal cancer: mucinous carcinoma on magnetic
resonance imaging indicates poor response to neoadjuvant chemoradiation. International
Journal of Radiation Oncology, Biology, Physics. 2012;82(2):842-8.
[7] Gaertner WB, Hagerman GF, Finne CO, et al. Fistula-associated anal adenocarcinoma: good
results with aggressive therapy. Diseases of the Colon & Rectum. 2008;51(7):1061-7.
[8] Inoue Y, Kawamoto A, Okigami M, Okugawa Y, Hiro J, Toiyama Y, et al. Multimodal-
ity therapy in fistula-associated perianal mucinous adenocarcinoma. American Surgeon.
2013;79(9):e286-8.
[9] Díaz-Vico T, Fernández-Martínez D, García-Gutiérrez C, Suárez J, et al. Mucinous adeno-
carcinoma arising from chronic perianal fistula: a multidisciplinary approach. Journal of
Gastrointestinal Oncology. 2019;10(3):589-96.
[10] Santos MD, Nogueira C, Lopes C. Mucinous adenocarcinoma arising in chronic perianal
fistula: good results with neoadjuvant chemoradiotherapy followed by surgery. Case Reports
in Surgery. 2014;2014:386150.
178/178