How would you treat a synchronous low rectal adenocarcinoma and anal squamous cell carcinoma with involved pelvic and inguinal nodes?

If the patient has intact bowel/anal sphincter function at baseline, I’d favor an organ-preserving approach. I’d treat with standard pelvic + inguinal chemoradiation with a dose/fractionation scheme isoeffective with 45 Gy in 25 fractions targeting pelvis/inguinals and a dose isoeffective with 54-56 Gy to gross disease. This could be achieved with a broad variety of sequential or simultaneous boost strategies spanning 25-30 fractions, with perhaps the most common being 45 Gy in 25 fx followed by a sequential boost to 54 Gy in 30 fx. I would use concurrent MMC plus either capecitabine or 5-FU. This patient also has an advanced rectal cancer with involved MRF as suggested in the comments. Pending assessment of treatment tolerance, consolidati...

Assuming that inguinal nodes are from anal SCC and the rectal tumor is pMMR, from the Medical Oncology perspective, starting treatment with Mitomycin-C and capecitabine concurrently with radiation would make sense. The patient might be benefited from systemic chemo (e.g., FOLFOX, or FOLFIRINOX if high-risk features with rectal cancer) after the radiation is completed, especially if the watch and wait for rectal cancer is pursued.

I've treated a couple of cases like this and would approach this case very differently from the posted answers. I think it is important to remember:

1. Unresectable anal cancer is curable with RT and appropriate chemotherapy.
2. Stage III rectal cancer is curable with preoperative RT, and chemotherapy. A minority of cases achieve a CR and may be managed with close surveillance and surgery only PRN. However, the majority (> ~2/3 of cases) won't achieve a CR but still have a decent chance of cure provided they undergo surgery. To cure the rectal cancer, you're probably going to need to include extirpative surgery to the pelvis.

The key in this case is the involved inguinal node(s). Assuming a biopsy confirms that the groin involvement is due to a...

Great discussion.

Just want to add one possible scenario.

In the clinic, for this type of situation, we usually would like to biopsy the inguinal lymph node and place fiducial in the node. The inguinal lymph node could be from the distal rectal adenocarcinoma especially if the distal rectal adenocarcinoma involves dentate line (Hamano et al., PMID 19912287. Technically, metastatic inguinal lymph node from rectal adenocarcinoma should be considered as distant metastatic disease (M1) although we still consider curative-intent treatment for this situation (Abd El Aziz et al., PMID 34953643).

Completely agree with Dr. @Dr. First Last that concurrent chemoradiation treatment with Mitomycin and fluoropyrimidine will cover both anal canal SCC and th...

Given the presentation of concurrent low-rectal adeno ca and anal SCC, the patient would not be a surgical candidate, therefore his treatment would be chemo and radiation, hoping there is no distant metastatic disease.

It would be important to know the size, HPV status, and stage of anal cancer. If anal cancer is HPV positive, then both cancers can be treated with chemo (MMC + cape) and radiation to a total dose of 55.8 Gy - see attached publication for HPV positive radiation dosing. (Chu et al., PMID 37456246)

However, if anal cancer is HPV negative then one would have to boost anal ca to 63 Gy and rectal cancer can be boosted up to 55.8 Gy after the initial 50.4 Gy for subclinical disease. I would recommend a sequential boost.

How would you treat a synchronous low rectal adenocarcinoma and anal squamous cell carcinoma with involved pelvic and inguinal nodes? The question does not provide details about the clinical stage and location, histopathologic details, MMR, and HPV status of both the rectal and anal tumors described: Were the two tumors described in question pure adenocarcinoma, pure squamous carcinoma, or were there adenosquamous components? Adenosquamous carcinomas of the colon and rectum are rare but well-described tumors in the literature with malignant glandular and squamous components capable of metastasizing, and they have been mostly managed similarly to anal cancer resulting in equivalent overall survival sparing patients from the additional morbid...