Accuracy of positron emission tomography/computed tomography and clinical assessment in the detection of complete rectal tumor regression after neoadjuvant chemoradiation

Abstract

BACKGROUND: Neoadjuvant chemoradiation (CRT) therapy may result in significant tumor regression in patients with rectal cancer. Patients who develop complete tumor regression have been managed by treatment strategies that are alternatives to standard total mesorectal excision. Therefore, assessment of tumor response with positron emission tomography/computed tomography (PET/CT) after neoadjuvant treatment may offer relevant information for the selection of patients to receive alternative treatment strategies. METHODS: Patients with clinical T2 (cT2) through cT4NxM0 rectal adenocarcinoma were included prospectively. Neoadjuvant therapy consisted of 54 grays of radiation and 5-fluorouracil-based chemotherapy. Baseline PET/CT studies were obtained before CRT followed by PET/CT studies at 6 weeks and 12 weeks after the completion of CRT. Clinical assessment was performed at 12 weeks after CRT completion. PET/CT results were compared with clinical and pathologic data. RESULTS: In total, 99 patients were included in the study. Twenty-three patients were complete responders (16 had a complete clinical response, and 7 had a complete pathologic response). The PET/CT response evaluation at 12 weeks indicated that 18 patients had a complete response, and 81 patients had an incomplete response. There were 5 false-negative and 10 false-positive PET/CT results. PET/CT for the detection of residual cancer had 93% sensitivity, 53% specificity, a 73% negative predictive value, an 87% positive predictive value, and 85% accuracy. Clinical assessment alone resulted in an accuracy of 91%. PET/CT information may have detected misdiagnoses made by clinical assessment alone, improving overall accuracy to 96%. CONCLUSIONS: Assessment of tumor response at 12 weeks after CRT completion with PET/ CT imaging may provide a useful additional tool with good overall accuracy for the selection of patients who may avoid unnecessary radical resection after achieving a complete clinical response.

High-dose chemoradiotherapy and watchful waiting for distal rectal cancer: a prospective observational study

“…These impressive results have since been corroborated by a case series from Maas et al 12 as well as a number of follow-up publications by the Brazilian group. 11,[22][23][24] The proportion of patients manageable by CRT alone varies between reports, as does the incidence of local recurrence for patients followed without surgery. This is at least to some extent likely due to differences in criteria for clinical complete response: The Mass et al series of 21 patients represented merely 11% of all rectal cancers treated with CRT in the study period, but only one of those 21 patients presented with an endoluminal recurrence during a median 15 months of follow-up.…”

“…It should be recognised, though, that comparisons between series are complicated by disparities in the use of supplementary chemotherapy, e.g. after CRT but prior to response evaluation 23 or after allocation to observation. 12 Overall, the results of the current study are comparable to the Brazilian reports, in terms of proportion of patients classified as complete responders as well as in incidence of local recurrence in the observation group.…”

Rectal cancer patients can be treated conservatively

“…It should be stressed that none of the imaging investigations such as CT, MRI or PET are enough accurate that they can be used to determine whether pCR was also achieved in cCR patients [32][33][34]. In the latter, pelvic MRI is rather an auxiliary aid, since diagnosing residual lesions does not exclude the diagnosis of complete regression [31].…”

Prediction of response to preoperative chemoradiotherapy in patients with locally advanced rectal cancer

“…Various PET-CT parameters have been investigated: mean standardized uptake value (SUVmean), maximum SUV (SUVmax), ΔSUVmax (SUVmax-pre -SUVmaxpost), response index [RI, (SUV pre -SUV post )/SUV pre ), metabolic tumor volume (MTV), ΔMTV% (MTV pre -MTV post )/MTV pre , visual response assessment (VRA), and total lesion glycolysis (TLG, SUVmean × MTV) ( Table 2) (19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32). These studies were able to establish a correlation between PET-CT results and CRT response (22)(23)(24)(25)(26)(27)(28)(29)(30). Most studies used several parameters but found just one or two parameters correlated with CRT response (21)(22)(23)(24)(25)(26)(27).…”

“…Second, PET-CT scans were not successful in determining nodal status (24). Third, PET-CT has difficulty in distinguishing between residual cancer and intraluminal or physiologic mucosal activity uptake (30). Fourth, the specificity of predictive value is too low to justify modification of the standard treatment protocol for an individual patient.…”