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Results of an Ontario Clinical Oncology Group (OCOG) prospective cohort study on the use of FDG PET/CT to predict the need for neck dissection following radiation

therapy of head and neck cancer (HNC)

Authors: Waldron JN, Gilbert RW, Eapen L, Hammond A, Hodson DI, Hendler A, Perez-Ordonez B, Gu C, Julian JA, Julian DH and MN Levine

Reviewed by Dr. Stephanie Snow

ASCO 2011 abstract 5504 Oral Session June 6, 2011

Date posted: June 2011

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Background

• Upwards of 50% of node-positive head and neck cancer (HNC) patients will have residual nodes visible on CT following curative intent radiation +/- chemotherapy

• ~1/3 of these will harbour residual cancer and can be cured by surgical neck dissection

• CT, MRI and US guided FNA have limited sensitivity and/or specificity in detecting residual nodal disease

• The question has been raised whether FDG-avidity on the post-therapy PET/CT can be used to better predict which patients are likely to need surgery:– 2 prospective case series reached differing conclusions

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Study Design

• Prospective multi-centre study performed at four regional cancer centres in Ontario, Canada with n=398

• Subjects:– Squamous cell HNC with N2 or N3 neck disease– Post-curative intent treatment with radiation +/- chemotherapy

with full dose radiation delivered to all suspected nodal disease– All subjects had CT and PET/CT performed before treatment

and 8-10 weeks post therapy• Intervention:

– All subjects with residual nodes >1cm axial dimension on post-treatment CT or positive PET-CT underwent neck dissection within four weeks of imaging

– Pathologic results of neck dissection were correlated with post treatment imaging

– Patients were then followed for two years

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Subject CharacteristicsCharacteristic Frequency

Sex Male Female

84%16%

Age (range) 27-84 (mean 57)

Primary Site Oropharynx Hypopharynx Larynx Oral cavity Unknown primary site

73%5%4%2%15%

Tumour Stage T0 T1-2 T3-4

15%48%37%

Nodal Stage N2a N2b N2c N3

15%43%33%10%

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RESULTS: PET/CT

Residual Disease Present

No Residual Disease Present

PET +ve 27 34

PET -ve 23 67

353 subjects had post therapy PET/CT scan at a mean of 9.2 weeks (range 4-19)

151 underwent a neck dissection

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RESULTS: PET/CT

Utility of PET/CT for Residual Nodal Disease

Sensitivity 54% (95% CI 40-67)

Specificity 66% (95% CI 57-75)

Positive Predictive Value 44% (95% CI 33-57)

Negative Predictive Value 74% (95% CI 65-82)

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RESULTS: CT

Residual Disease Present

No Residual Disease Present

CT +ve 47 90

CT -ve 3 14

154 patients who had a post-treatment CT underwent a neck dissection

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RESULTS: CT

Utility of PET/CT for Residual Nodal Disease

Sensitivity 94% (95% CI 84-98)

Specificity 13% (95% CI 8-21)

Positive Predictive Value 34% (95% CI 27-43)

Negative Predictive Value 82% (95% CI 59-94)

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STUDY COMMENTARY

• Largest prospective trial to address this question to date• Canadian data • There is significant potential for functional impairment

and compromise in quality of life after a neck dissection• A test with high sensitivity and negative predictive value

could help predict who does NOT have residual disease• In this trial, enhanced CT scan was superior to PET/CT

in sensitivity and negative predictive value, and the authors concluded that PET/CT should NOT be used to determine need for neck dissection

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BOTTOM LINE FOR

CANADIAN MEDICAL ONCOLOGISTS

• This trial does not provide evidence for a clear role of PET/CT to assess for nodal disease post HNC therapy, however, the conclusion that PET/CT should not be used in neck dissection decisions may be pre-mature

• This is a question that is still important to explore as there were a number of potentially confounding issues:– Impact of HPV status on radiographic nodal response rates is

unknown and could have been important in this study with 73% oropharyngeal primaries

– Optimal timing for post-treatment PET/CT – the positive prospective trial did PET/CT at 12 weeks