Watch and Wait (Nonoperative Management)

Organ-preservation strategy for Rectal Cancer patients who achieve a complete or near-complete response to neoadjuvant therapy: deferral of surgery in favor of active surveillance, avoiding the morbidity, mortality, permanent-stoma risk, and functional consequences of proctectomy. Content below is from a textbook reference chapter (ASCRS Ch28 - Rectal Cancer Nonoperative Management), not primary literature. See Total Neoadjuvant Therapy (TNT)'s "Surgery and non-operative management (NOM)" section for this wiki's existing primary-literature-sourced content on NOM eligibility and relapse rates (locoregional relapse 20–40%, distant metastatic risk 5–15%, the OPRA trial's TME-free survival data) — that content remains authoritative for those figures and is cross-linked, not duplicated, below.

Terminology and definitions

• Pathologic complete response (pCR): reserved for ypT0N0 tumors in patients who had a proctectomy, or for ypT0 tumors after a full-thickness local excision without radiological evidence of mesorectal positive nodes or deposits.
• Clinical complete response (cCR): no evidence of tumor on clinical, endoscopic, and radiological exams.
• Watch and Wait (WW): originally used exclusively for patients who achieved a cCR and were offered no immediate surgery, with strict and close surveillance — achieving a cCR is a prerequisite for entering a WW program.
• Local regrowth: reappearance of tumor in the rectal wall or regional lymph nodes after an apparent cCR — occurs more often in the bowel wall than the regional lymph nodes and is therefore more easily detected by DRE/flexible sigmoidoscopy than distant disease. Most regrowths are potentially salvageable by surgery.
• Local recurrence: any tumor reappearance in the pelvis after a curative-intent surgery (i.e. after proctectomy, not applicable to a still-nonoperative WW patient).
• Induction vs. consolidation chemotherapy: chemotherapy given before CRT is induction chemotherapy; chemotherapy given during and after CRT (before surgery) is consolidation chemotherapy — see Total Neoadjuvant Therapy (TNT)'s Consolidation vs. induction chemotherapy sequencing section for the fuller trial evidence on this distinction.

Rationale

The possibility of a permanent stoma is a major concern for rectal cancer patients — impacting body image and quality of life, with perspectives varying across geography/culture. The concept of avoiding surgery after neoadjuvant chemoradiation was driven by the observation of pCR in patients treated with abdominoperineal resection (permanent colostomy), following similar observations from anal cancer treatment (avoidance of radical surgery after complete tumor regression with favorable oncologic outcomes). Most rectal cancer patients have more surgical options than anal cancer patients (for whom APR is the main radical alternative) — many are candidates for sphincter-preserving procedures, but restorative proctectomy itself is often associated with significant bowel dysfunction, worsened by prior pelvic radiation. A sizeable fraction of patients who undergo a restorative procedure with temporary diverting stoma reversal are left with variable fecal incontinence and low anterior resection syndrome (LARS), some requiring conversion to a permanent stoma or cecostomy/appendicostomy for antegrade colon lavage (see Low Anterior Resection Syndrome (LARS)). Proctectomy, with or without sphincter preservation, also carries significant sexual and urinary functional consequences, plus immediate postoperative morbidity/mortality despite minimally invasive approaches, and substantial financial/social burden (stoma supplies, activities-of-daily-living assistance, professional-life impact).

Primary tumor assessment and selection criteria

Baseline tumor assessment (DRE, endoscopic features, radiological imaging) is paramount for patients being considered for organ preservation; neoadjuvant therapy should only start after these studies are complete and confirmatory biopsy of adenocarcinoma has been obtained and documented.

• Accidental vs. intentional WW: attempts to cure rectal cancer with radiation alone date to the early twentieth century, when surgical mortality/morbidity was prohibitive. Over the years, some surgeons omitted surgery in patients with an apparent complete/near-complete response because of advanced age, high surgical risk, or patient refusal of a permanent stoma — this "accidental" WW approach should be distinguished from the systematic/intentional approach, in which patients with distal rectal cancer likely requiring a low colorectal/coloanal anastomosis or a permanent colostomy are identified, restaged, and selectively entered into a WW protocol with the explicit intent of achieving permanent organ preservation.
• Baseline stage: an important predictor of tumor response — more advanced tumors are less likely to completely respond to nCRT. Current guidelines recommend nCRT for locally advanced tumors with baseline features indicative of high local-recurrence risk after proctectomy alone: mesorectal- fascia distance ≤1mm (mrCRM+, including T3c,d or T4), extramural venous invasion (EMVI+), extensive nodal disease (N1c/N2), or lateral pelvic sidewall nodes (LPNM+). These features are not a WW contraindication, but a cCR is less likely in such advanced tumors, and clinical/radiological identification of a cCR can be challenging in the presence of extensive disease (difficulty distinguishing fibrotic change from residual tumor).
• Intermediate disease (mrT3a,b or N0/1 without additional high-risk features): the indication for nCRT is controversial. Such patients remain candidates under TNM-based international guidelines (e.g. NCCN), but data from the MERCURY trial suggest these patients are at low risk for local recurrence after proctectomy alone, casting doubt on the need for nCRT — offering nCRT to patients with more distal intermediate-stage tumors specifically offers the possibility of a cCR and organ preservation.
• Early-stage disease (mrT1/T2N0): local recurrence risk with proctectomy alone is very low, so these tumors aren't typically nCRT candidates. However, nCRT followed by local excision has been proposed as an alternative for early-stage distal rectal cancer that would otherwise need a coloanal anastomosis or permanent colostomy — several phase II trials have shown a higher pCR rate for these patients than for more advanced disease (see Local Excision of Rectal Neoplasms's Adjuvant and neoadjuvant therapy section, e.g. ACOSOG Z6041). It's therefore reasonable to offer WW to early-stage patients seeking to avoid a permanent stoma who start treatment with nCRT in an attempt to achieve a cCR.

Tumor location

Any rectal cancer patient with a cCR after CRT is a potential WW candidate, but patients most likely to benefit are those who would otherwise need a low colorectal/coloanal anastomosis or a permanent colostomy — i.e. tumors in the distal rectum, which are also more accessible to monitoring by DRE. mrT2 cancers beyond the reach of DRE are probably surrounded by mesorectal fat and less likely to have CRM positivity/local recurrence if treated with upfront sphincter-sparing surgery — these patients are less likely to benefit from organ preservation (an exception: an obese patient with a long anal canal, whose tumor sits immediately above the anorectal ring, may be just beyond DRE reach but still a WW candidate). MRI provides valuable information about the tumor's relationship to the sphincter complex, levator muscles, prostate, seminal vesicles, vaginal wall/cervix, and anterior peritoneal reflection — helping anticipate permanent-stoma need, sphincter-sparing feasibility, and anastomosis type if proctectomy is ultimately needed, and useful for WW patient selection. In summary: patients with lower tumors requiring a low colorectal or hand-sewn coloanal anastomosis or an APR are more likely to benefit from a WW strategy and organ preservation; patients with more proximal tumors carrying a low local-recurrence risk are unlikely to benefit from organ preservation and are better treated with upfront proctectomy.

Endoscopic features such as pit pattern and submucosal vascular architecture can help identify benign lesions or superficially invasive rectal cancers that fulfill criteria for endoscopic submucosal resection (see Colorectal Polyps, ASCRS Ch23 - Management of Malignant Polyps) or transanal local excision (see Local Excision of Rectal Neoplasms) without the need for proctectomy or nCRT at all.

Assessment of tumor response

Response depends on tumor characteristics (size, stage, some genomic features) and treatment variables (radiation fractionation dose, time from radiotherapy completion). In a WW program, tumor response is assessed with the same diagnostic tools used for initial staging: DRE, endoscopy, and radiology (preferably MRI).

• The 6-week interval between end of nCRT and surgery (in patients with stage II–III rectal cancer treated with CRT and proctectomy) has been shown effective for surgical technical difficulty and perioperative morbidity, associated with a pCR rate of approximately 18%. Retrospective studies suggest longer radiotherapy-to-surgery intervals result in higher pCR rates. Growing evidence suggests tumor response is time-dependent and probably nonlinear — implying that tumors without a cCR at the initial 6–8 week assessment may still achieve a cCR with longer observation, and that adding chemotherapy during a longer observation period increases the likelihood of cCR and organ preservation.
• Current WW strategy: assess tumor response 6–8 weeks after completion of neoadjuvant therapy, then stratify patients into one of three groups (per the chapter's Table 28.1):

Patients with an incomplete response — even with significant tumor shrinkage — typically undergo surgery. Patients with a cCR enter a standard WW surveillance protocol with repeat assessments every 3–4 months. Patients with a significant but not-quite-complete response (near-complete) enter an intensive surveillance protocol with reassessment in 8–12 weeks. Most patients achieve all strict cCR criteria within 28–34 weeks after completing radiotherapy; it may take up to a year (52 weeks) for some tumors. A lack of continued response evidence across any of the three diagnostic modalities, or any sign of tumor regrowth, is an indication for surgery.

Criteria for a complete clinical response

Based on three pillars of assessment: clinical (DRE — regular mucosal surface, only minor induration allowed, no significant abnormalities), endoscopic (whitening of the mucosa with telangiectasias, absence of ulceration/mass/stenosis), and radiological (MRI — presence of low-signal intensity at the original tumor location on T2W images = mrTRG1; absence of diffusion restriction on DW imaging). Endoscopic biopsy is not required to enter a WW protocol for patients with a cCR — given the random distribution of any residual cancer cells across rectal-wall layers post-nCRT, endoscopic biopsies aren't very useful for response assessment: a negative biopsy cannot exclude residual tumor in near-complete/incomplete responders, and risks giving patients a false sense of security that could lead them to refuse a recommended operation. Combining all three modalities increases accuracy — Maas et al. found that when DRE, endoscopy, and MRI were all consistent with absence of residual tumor, the accuracy of predicting a complete response was 98%. The OPRA trial (see Total Neoadjuvant Therapy (TNT)) uses a similar three-tiered response-assessment schema (DRE, endoscopy, T2/diffusion-weighted MRI); studies validating the reproducibility of that schema are underway.

Radiological studies

Endorectal ultrasound (ERUS) was originally used for both baseline staging and response assessment, providing good accuracy for identifying complete response in the primary tumor (ypT status); patient discomfort and difficulty assessing mesorectal disease away from the rectal lumen contributed to its replacement by MRI. MRI is now the imaging modality of choice — high-resolution protocols, synoptic reporting, and T2-weighted images are usually sufficient for response assessment and WW-candidate identification; response is graded using the mrTRG scale, analogous to pathologic tumor-regression-grade systems (mrTRG1 = maximal regression, mrTRG5 = no regression); strict cCR criteria require mrTRG1 within the original tumor area. Diffusion-weighted imaging (DWI) provides functional information via restricted water-molecule movement (confirmed on apparent-diffusion-coefficient maps), which is highly suspicious for residual cancer cells and can help confirm cCR or residual disease. PET/PET-CT: early studies were disappointing, but more recent data supports a role in WW patient selection — a decrease in standard uptake value and metabolic tumor volume between baseline and posttreatment studies appears to be the best predictor of response by PET/CT.

Endoscopic and clinical assessment

Historically, the earliest WW reports predated standardized radiological imaging and relied mostly on clinical (DRE) and endoscopic assessment. DRE can be challenging for distinguishing cCR from residual disease — surgeons involved in organ-preservation programs should examine patients by DRE both at baseline and during response assessment. Endoscopically, a cCR should show a smooth, regular mucosal surface; slight rectal-wall induration may be palpable, but ulcerations, nodules, masses, or stenosis should raise suspicion for residual disease and are not appropriate for WW. Flexible endoscopy provides improved visualization, more accurate documentation, better training, and better patient comfort compared to rigid proctoscopy (though rigid proctoscopy may suffice for identifying a cCR under strict criteria); retroflexion and magnifying/narrowband imaging can provide additional advantages, particularly near the dentate line.

Surveillance/follow-up strategy

Multiple published series report WW outcomes using different surveillance protocols, varying mostly in subtle details — schedules need to address both local-regrowth risk and distant-metastasis risk. The actuarial rate of local regrowth at 3 years may reach nearly 30%, with most regrowths detected within the first year — most follow-up schedules therefore recommend more intensive/strict surveillance during this initial period.

• Local reassessment after cCR: intensive surveillance is needed especially during the first 2 years after cCR is achieved. Tumor response is typically reassessed by clinical and endoscopic measures every 3 months; MRI has been progressively incorporated and is now recommended every 6 months during the first 2 years. Conditional-survival data suggest that once a cCR has been sustained for 2 years, local-regrowth risk is low (≤10%), making intensive follow-up less critical beyond that point — after 2 years, reassessment every 6 months for a further 3 years is typical. The need for additional surveillance beyond 5 years remains an unanswered question; some series have reported regrowth detection as late as 7 years after nCRT completion, leading some programs to recommend yearly monitoring indefinitely within a survivorship program.
• Surveillance for metastatic and metachronous disease: cCR patients remain at risk for metastatic disease and metachronous colorectal cancer; surveillance generally follows the same recommendations as for any colorectal cancer patient, preferably with CT of the chest, abdomen, and pelvis (see Rectal Cancer's Survival, surveillance, and adjuvant chemotherapy section for the general CRC surveillance schedule). Restaging CT is particularly important for initial-cCR patients who go on to develop local regrowth, since they appear to be at higher risk for metastatic disease. Endoscopic colon surveillance (full colonoscopy) should follow the guidelines for patients at high risk for developing colorectal cancer (i.e. those with a personal history of CRC).

Local regrowth

The actuarial rate of local regrowth at 2 years is around 25%, following an exponential curve with most recurrences detected during the first year of follow-up. The vast majority of local regrowths have an endoluminal component and are therefore amenable to endoscopic and/or clinical detection during active surveillance; a small percentage are detected exclusively outside the rectal wall (mesorectal or lateral pelvic sidewall disease). The only established risk factor for local regrowth is baseline clinical T stage: one study and an individual-participant-data meta-analysis suggest that for every increase in baseline cT stage (cT2, cT3, cT4), there is a 10% increase in regrowth risk (20%, 30%, and 40% respectively). This influence of baseline cT stage on regrowth risk appears restricted to the first 2 years after cCR — based on conditional-survival estimates, the risk of local regrowth/recurrence after a cCR sustained beyond 2 years appears independent of baseline cT stage.

Systematic reviews of retrospective studies suggest nearly 90% of local regrowths are amenable to R0 salvage resection; in most cases, salvage surgery is a proctectomy. Patients undergoing salvage proctectomy have similar rates of R0 margins, postoperative morbidity, and oncologic outcomes as patients who undergo proctectomy within 8–12 weeks after an incomplete response to nCRT (i.e. never entering WW at all). Transanal local excision may also be a salvage option for tumor regrowth in patients with baseline early disease (cT2N0) entered into a WW protocol; however, transanal local excision is not routinely offered as the primary salvage surgical option for tumor regrowth in patients with baseline clinical stage II or III disease entered into WW.

Systemic recurrences

Overall, patients with a cCR managed nonoperatively appear to have lower rates of distant metastases than patients with an incomplete response to neoadjuvant treatment. Most studies comparing cCR-WW patients to pCR-after-radical-surgery patients indicate no differences in distant-metastasis rates — suggesting no added benefit of radical surgery in preventing M1 disease in these patients. This is particularly notable given that WW-cCR patients did not routinely receive adjuvant chemotherapy, whereas nearly 50% of pCR-after-radical-surgery patients did. Patients with local regrowth after a cCR appear to be at increased risk for distant metastasis compared to patients with no regrowth after a cCR — it's possible that regrowth reflects a more aggressive tumor biology, which may partly explain the metastasis-rate difference. It remains unclear whether an up-front proctectomy would have prevented development of metastatic disease in patients who underwent WW instead.

Oncologic outcomes

The current evidence on WW safety/efficacy is based on retrospective institutional case series, with several acknowledged limitations: strong potential for selection bias, heterogeneous patient selection/imaging/regimens/response-assessment timing, and inconsistent (often non-prospectively- defined) response criteria; total patient numbers within study periods are not always consistently reported, further complicating estimation of the true denominator of patients who might benefit from organ preservation. The ideal study — a randomized trial of WW vs. proctectomy in patients with a cCR — is considered unlikely to be feasible, since it's unlikely that patients with a cCR will agree to randomization between WW and proctectomy. The OPRA trial (organ preservation in rectal adenocarcinoma) is prospectively investigating the impact of WW on disease-free survival for patients with clinical stage II–III rectal adenocarcinoma treated with total neoadjuvant therapy — see Total Neoadjuvant Therapy (TNT) for that trial's TME-free survival figures.

Some studies have compared survival of cCR-WW patients to patients of similar clinical stage treated with neoadjuvant therapy and proctectomy who achieved a pCR: patients treated with proctectomy had better disease-free survival compared with WW (pooled HR 0.47, 95% CI 0.28–0.78); there was no difference in overall survival between groups. The DFS difference here is mainly driven by the risk of local regrowth, where the possibility of salvage resection ranges from 80% to 100% (see Local regrowth above).

Functional outcomes

Very few studies have specifically assessed functional outcomes in WW patients. There appear to be significant differences in quality of life and anorectal/sexual/urinary function between proctectomy patients and WW patients. Patients with a sustained cCR after 2 years of WW had better quality of life and general health (SF-36, EORTC QLQ-C30), fewer defecation problems (Vaizey and LARS scores), fewer urinary problems (International Prostate Symptom Score), and better sexual function (EORTC QLQ-C30) compared with a matched proctectomy group. However, one third of WW patients still had considerable symptoms associated with low anterior resection syndrome despite avoiding proctectomy entirely — suggesting a potential effect of nCRT itself on functional outcomes, independent of surgery. WW patients also had superior functional outcomes compared with patients who underwent local excision after nCRT, based on fecal incontinence scores and anorectal manometry.

Prediction of tumor response

An accurate tool for predicting sustained tumor response to neoadjuvant therapy would improve patient selection for WW and help avoid overtreating patients unlikely to respond (who might otherwise proceed directly to proctectomy without a WW attempt).

• Genomic markers: individual gene mutations and genomic instability have been associated with tumor response to nCRT. Microsatellite instability (MSI) phenotype (found in ≤5% of all rectal cancers) was suggested by a large institutional series to be more sensitive to nCRT than microsatellite-stable tumors, but this was not confirmed in a retrospective review of the National Cancer Database. Tumors with K-ras or K-ras/p53 mutations appear more resistant to nCRT. These genetic alterations may help identify a subset of patients less likely to achieve a cCR, but provide no WW-relevant information for the majority of rectal cancer patients (who don't carry these specific mutations).
• Gene-expression-profile-based prediction has been largely unsuccessful — significant intertumoral and intratumoral heterogeneity produces gene signatures with very low overlap and inaccurate separation of poor from good responders.
• A DNA-repair-gene-based prediction score has recently been suggested for this purpose: a low score was associated with poor nCRT response regardless of the DNA-expression platform used, observed in nearly 40% of patients tested, and a low score resulted in poor response to nCRT in 70–90% of cases. Modeled in consecutive cT2N0 patients specifically, using this strategy is projected to result in avoidance of unnecessary nCRT in 36% of patients, restriction of nCRT to 60% of patients, and good response with organ-preservation possibility in nearly 75% of cases.
• Patient-derived rectal cancer organoid cultures ("tumoroids") appear to retain molecular features of the primary tumors from which they're derived, and their ex vivo responses to chemotherapy and radiation correlate with the clinical responses observed in individual patients' tumors. Future studies using this ex vivo platform may help develop an algorithm for more accurate WW-candidate selection.

Related pages

• Rectal Cancer — staging, the German Rectal Cancer Study/TME/CRM evolution-of-treatment history, and the brief origin-of-WW mention this page substantially expands.
• Total Neoadjuvant Therapy (TNT) — the neoadjuvant regimens (CRT/SCRT, chemotherapy sequencing) that precede WW candidacy; that page's own NOM section remains authoritative for primary- literature-sourced NOM relapse-rate figures and the OPRA trial's TME-free survival data.
• Local Excision of Rectal Neoplasms — the local-excision option this page references both as an alternative to WW for early distal disease and as a possible salvage option for regrowth.
• Colorectal Cancer Staging (TNM) — CRM and EMVI formal definitions underlying this page's patient-selection criteria.
• Low Anterior Resection Syndrome (LARS) — the functional syndrome this page's Rationale and Functional outcomes sections reference.

Open items / gaps

• No primary literature yet on any of this page's figures (all textbook-secondary-source-level, per ASCRS Ch28 - Rectal Cancer Nonoperative Management) — the OPRA trial itself is referenced by name in both this chapter and Total Neoadjuvant Therapy (TNT), but its own primary publication is not independently ingested on this wiki.
• The DNA-repair-gene prediction score and patient-derived organoid research described under Prediction of tumor response are both described as recent/emerging — worth revisiting if either matures into a validated clinical tool covered by later literature.
• MERCURY trial (cited here as evidence against routine nCRT for intermediate-risk mrT3a,b/N0-1 disease) is not independently ingested — referenced only via this chapter.