How Do We: Assess Tumor Response To Treatment?

Mr P, who is currently undergoing palliative chemotherapy metastatic rectal cancer (liver, lung), came to review his CT restaging after cycle 6 chemotherapy.

Four liver lesions, previously 2.5cm, 2cm, 1cm, 0.5cm showed only slight reduction in size to 2.2cm, 1.5cm, 1cm, 0.5cm. Lung lesions,  previously 2cm and 1cm show slight reduction also in size to 1.5cm, 1cm.

He was worried because of the minimal changes in tumor after treatment.

Why is it important to assess tumor response?

For me mainly, it’s to avoid harming patients.

  • Harms from continuing chemotherapy that is ineffective and allowing the tumor to continuously grow and spread. Also, patients will be still exposed to all the side effects and risks of chemotherapy/ targeted therapy.
  • Harms from stopping treatment early when patient is responding well to the treatment.

CT restaging

Assessment of tumor response is by repeating CT scans/ CT restaging at mid-cycle (eg. if total of 12 cycles of chemotherapy is planned, it’s requested at cycle 6) palliative chemotherapy to assess tumor response.

  • CT scan of the thorax, abdomen, pelvic is normally requested for GI malignancy.
  • CT brain/base of skull, neck, thorax is normally requested for head and neck malignancy.

CT restaging is not required for patients undergoing adjuvant chemotherapy (unless there is suspicious lesion needing confirmation) as there is no more tumor after curative surgery (eg. early breast, colorectal cancer).

  • Yearly CT restaging might be more benefits and cost effective to follow up on the disease which is in remission.
  • Referral back to primary team such as ENT or gynaecology is more important as they can help to detect disease recurrence at earlier stage via nasal endoscope, vaginal examination, pap smear, etc.
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RECIST

In order to assess tumor response, after CT restaging was done, for the case above, lesions we assessed using RECIST 1.1 criteria to decide the response;

  • Partial response (PR): At least a 30% decrease in baseline sum of diameters (BSD) of target lesions, taking as reference the baseline sum diameters.
  • Complete response (CR): Disappearance of all target lesions. Any pathological lymph nodes size reduced in short axis to <10 mm.
  • Progressive disease (PD): At least a 20% increase in baseline sum of diameters (BSD) of target lesions or new lesion appears.
  • Stable disease (SD): Neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD (changes in baseline sum of diameters not less than 30% and not more than 20%)

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To get the baseline sum of diameters (BSD), take two lesions only from each organ (max 5 organs, 10 measurements). Using example from the above:

  • Initial: 2 largest lesions from liver (2.5cm+2cm) and 2 largest lesions from lung (2cm+1cm) = BSD 7.5cm
  • Mid-cycle treatment: liver lesions (2.2cm+1.5cm) and lung lesions (1.5cm+1cm) = 6.2cm
  • Reduction in size is 1.3cm (-17%); stable disease (SD)

As long as there is partial response or stable disease, these indicate treatment is still effective and can be continued. Treatment will be stopped if there is progressive disease and switched to other second- or third-line treatments.

Tumor markers

Certain tumor markers can be used to assess response to treatment, only and especially if their level was high before treatment.

It’s can be repeated at every cycles or alternate cycles and able to assess response earlier (rather than mid-cycle of treatment) and cost less than CT restaging.

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Tumor markers and their corresponding cancers

Clinical improvement

Finally, last but not least, and perhaps most important is assessment of any clinical improvement after treatment.

As palliative treatment/ chemotherapy is aim to palliate symptoms and improve patient general well being, it’s of no use if patient’s condition worsened despite on treatment.

One of my patient with metastatic oesophageal cancer (lung, non-regional lymph nodes) main complain was dysphagia and he unable to tolerate even fluids. After first cycle palliative chemotherapy, he was able to tolerate a bit of fluids and after third cycle, he was able to tolerate porridge.

These improvements showed that treatment is obviously working and I did not even proceed with CT restaging mid-cycle of his chemotherapy to save unnecessary investigation.

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