Squamous cell carcinoma of the anus is a very rare but extremely debilitating tumor and only accounts for about 2% of all gastrointestinal tumors (1–4). However, the incidence appears to have increased slightly over the last decade. Due to the high chemosensitivity of squamous cell carcinoma chemoradiation is the treatment of choice compared to invasive surgical procedures (5, 6).

Nevertheless, the optimal treatment remains controversial given the sometimes exorbitant toxicity of chemotherapeutical drugs such as mitomycin and radiation therapy.

Many attempts have been made to reduce toxicity, with intensity-modulated radiation therapy bringing some improvement, whereas a quantitative reduction in chemotherapy by lowering the effective levels also reduces the therapeutic effect.

Hypoxic pelvic perfusion increases the sensitivity of some chemotherapeutic agents (e.g. cis platinum). Additionally limiting the chemotherapy exposure to the pelvic region reduces systemic toxicity which in turn minimizes systemic side effects.

Early case reports suggest that hypoxic pelvic perfusion can lead to high local response rates of rectal cancer (7).

However, hypoxic pelvic perfusion alone is limited by the challenge of ensuring complete tumor coverage.

Electroporation increases cell membrane permeability therefore enhancing chemotherapy drug effectiveness. Several clinical studies have shown that electroporation can enhance the local response however it is often limited by the depth of the tumor and the ability to treat larger more deeply seated tumors combining hypoxic pelvic perfusion and electroporation overcomes the limitation of each approach (8).

Astoundingly higher cytostatic drug levels and therefore greater effectiveness can be achieved through isolated pelvic regional perfusion with comparatively lower cytostatic drug dosages.

We present a series of four HPV-positive patients with anal cancer, two with malignancy grade G3 primary tumors, and two with recurrent G2 tumors. In the latter two cases there was a relapse after primary radiochemotherapy.

Patient characteristics according to diagnosis, histology, previous treatment and type of therapy are listed in Table 1 .

Historically, the primary treatment for anal cancer was abdominoperineal resection (APR), a radical surgery leaving patients with a permanent colostomy. This was standard through the mid-20^th century, though it had significant drawbacks: high morbidity, poor quality of life, and a risk of cancer recurrence. The 5-year survival rate was approximately 50% (3, 9). When used as a salvage surgery after failed CRT the 2-year OS is ~60%, but 5-year OS drops to ~24.5%.

A major breakthrough came in the late 1970s and early 1980s with the introduction of the Nigro protocol, a pioneering approach combining radiation therapy with chemotherapy (5-fluorouracil and mitomycin C) (10–12). This approach demonstrated that many patients could achieve complete remission without surgery. As a result, chemoradiation became the standard of care, allowing for organ preservation. Local control is achieved in 68 - 84%, colostomy-free survival in 65 - 75% and 5-year OS in 65 – 79% (4, 13–17).

Acute toxicities are common: hematologic (cytopenias), mucocutaneous, gastrointestinal, genitourinary symptoms. Late effects may include chronic bowel dysfunction, sexual dysfunction, infertility, or chronic pain. Even local excision alone of stage I anal cancer can be effective and curative. However, careful follow-up is required because the 5-year progression-free survival after combination with radiochemotherapy is slightly better at 91 versus 83% for local excision (18). Radiochemotherapy regimens consisting of 5-fluorouracil and mitomycin and concomitant radiation achieved stage-dependent 5-year survival rates of up to 90% and sphincter preservation of up to 80% (12, 19) while avoiding rectal amputation (20, 21). Despite these excellent clinical results (15), the severe toxicity with mandatory interruption of therapy clouds the overall picture in approximately half of the cases.

Precisely because of the good clinical results in the face of intolerable side-effects such as nephrotoxicity or pulmonary fibrosis, attempts were made to modify the treatment regimens, using immunotherapy (22–24), new drugs such as capecitabine or paclitaxel, or intensity – modulated radiotherapy (25–27), to improve quality of life while maintaining clinical outcomes.

Isolated perfusion therapy can be viewed as a further step in terms of both intensifying therapy and minimizing or eliminating side effects. It can be applied to all body regions (28) or segments in the form of an isolated circuit.

For hypoxic perfusion, which we prefer to use, mitomycin is best suited as a very potent chemotherapeutic agent for gastrointestinal tumors because of its up to tenfold increase in cytotoxicity under hypoxic conditions. The same applies to doxorubicin. The efficacy of Cisplatin is not affected. All other common chemotherapy drugs have reduced cytotoxicity under hypoxia (29).

The high effective concentrations of cytostatics are achieved on the one hand by the low blood volumes in the perfusion circuit, but above all by the application of the cytostatics as a short-term arterial infusion into the isolated perfusion circuit. The high influx concentration of chemotherapy drugs over seven to twelve minutes leads to high uptake in the tumor tissue. This short-term intra-arterial infusion procedure has been shown to be effective in squamous cell carcinomas such as head and neck cancer (30, 31), in advanced cervical cancer (32), and more recently in anal cancer. Even in advanced osteosarcoma, complete remission can be achieved due to high local drug exposure using a technical variant (33).

In the two previously untreated patients, three and two isolated perfusion therapies were necessary; in the case of previous radiochemotherapy and recurrences as in cases two and four, repeated intra-arterial infusion alone was not sufficient because the local cytostatic exposure was too low. Only isolated pelvic perfusion in combination with electroporation achieved a histological complete remission ( Table 2 ) due to increased cytostatic drug uptake via temporarily porous tumor cell membranes as a result of the electrical impulses (34).

The dosages of chemotherapeutic agents used by us under locoregional perfusion chemotherapy are very different from those under systemic chemotherapy. The smaller treated volume and, above all, the only short-term intra-arterial application of the chemotherapeutic agent generate the required local exposure with the necessary high concentration. Therefore, the effectiveness of the therapy cannot be assessed based on the total dose used but rather based on the effective concentration over time. The total dose of cisplatin used in the present isolated pelvic perfusions is only 50 to 70 mg, of mitomycin 10, max 15 mg with, however, very effective local exposure with short-term intra-arterial infusion into the perfusion circuit.

On the one hand, chemofiltration after application of the cytostatics reduces the low toxicity of low-dose chemotherapeutic agents, but primarily prevents cumulative toxicity from occurring too quickly, especially from substances with cumulative toxicity such as mitomycin and doxorubicin.

Even though the number of cases is of course far too small and no binding statement can be made, it turns out that all four patients tolerated the therapies largely without any symptoms and no relevant adverse events in the sense of systemic toxicity occurred. The recurrence- free times in full remission are currently 48, 27, 10 and 8 months.

The present case series was simply intended to demonstrate that it is fundamentally possible to apply a proven, highly effective approach such as mitomycin compounds to squamous cell carcinoma, in this case anal carcinoma, using regional therapeutic methods that are modified to largely avoid disruptive and distressing adverse events. Isolated hypoxic pelvic perfusion and electrochemotherapy for anal cancer with short-term arterial infusion of chemotherapy drugs into the arterial perfusion line together produce highly effective drug exposure leading to complete remission. The subsequent blood purification using chemofiltration largely avoids toxic side effects and cumulative toxicity.

Isolated hypoxic pelvic perfusion combined with electroporation is an effective, low-toxicity valid alternative to traditional therapies for the treatment of anal squamous cell carcinoma.