Positive clinical experience with misonidazole in brachytherapy and external radiotherapy

The tumour microenvironment after radiotherapy: mechanisms of resistance and recurrence

Radiotherapy plays a central part in curing cancer. For decades, most research on improving treatment outcomes has focused on modulating radiation-induced biological effects on cancer cells. Recently, we have better understood that components within the tumour microenvironment have pivotal roles in determining treatment outcomes. In this Review, we describe vascular, stromal and immunological changes that are induced in the tumour microenvironment by irradiation and discuss how these changes may promote radioresistance and tumour recurrence. We also highlight how this knowledge is guiding the development of new treatment paradigms in which biologically targeted agents will be combined with radiotherapy.

Microenvironment and radiation therapy

Dependency on tumor oxygenation is one of the major features of radiation therapy and this has led many radiation biologists and oncologists to focus on tumor hypoxia. The first approach to overcome tumor hypoxia was to improve tumor oxygenation by increasing oxygen delivery and a subsequent approach was the use of radiosensitizers in combination with radiation therapy. Clinical use of some of these approaches was promising, but they are not widely used due to several limitations. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that is activated by hypoxia and induces the expression of various genes related to the adaptation of cellular metabolism to hypoxia, invasion and metastasis of cancer cells and angiogenesis, and so forth. HIF-1 is a potent target to enhance the therapeutic effects of radiation therapy. Another approach is antiangiogenic therapy. The combination with radiation therapy is promising, but several factors including surrogate markers, timing and duration, and so forth have to be optimized before introducing it into clinics. In this review, we examined how the tumor microenvironment influences the effects of radiation and how we can enhance the antitumor effects of radiation therapy by modifying the tumor microenvironment.

How can we overcome tumor hypoxia in radiation therapy?

Local recurrence and distant metastasis frequently occur after radiation therapy for cancer and can be fatal. Evidence obtained from radiochemical and radiobiological studies has revealed these problems to be caused, at least in part, by a tumor-specific microenvironment, hypoxia. Moreover, a transcription factor, hypoxia-inducible factor 1 (HIF-1), was identified as pivotal to hypoxia-mediated radioresistance. To overcome the problems, radiation oncologists have recently obtained powerful tools, such as "simultaneous integrated boost intensity-modulated radiation therapy (SIB-IMRT), which enables a booster dose of radiation to be delivered to small target fractions in a malignant tumor", "hypoxia-selective cytotoxins/drugs", and "HIF-1 inhibitors" etc. In order to fully exploit these innovative and interdisciplinary strategies in cancer therapy, it is critical to unveil the characteristics, intratumoral localization, and dynamics of hypoxia/HIF-1-active tumor cells during tumor growth and after radiation therapy. We have performed optical imaging experiments using tumor-bearing mice and revealed that the locations of HIF-1-active tumor cells changes dramatically as tumors grow. Moreover, HIF-1 activity changes markedly after radiation therapy. This review overviews 1) fundamental problems surrounding tumor hypoxia in current radiation therapy, 2) the function of HIF-1 in tumor radioresistance, 3) the dynamics of hypoxic tumor cells during tumor growth and after radiation therapy, and 4) how we should overcome the difficulties with radiation therapy using innovative interdisciplinary technologies.

Treatment of local recurrences of rectal carcinoma

From 1978-1992, 159 patients were treated for local recurrences of rectal carcinoma. They could be subdivided into three groups according to the type of primary treatment given; 82 patients underwent primary surgery without irradiation, 37 patients had preoperative and 40 patients postoperative radiotherapy. The localizations of the recurrences and the curative and palliative potentials of surgery and radiotherapy in the treatment of local recurrences were studied. There was no difference in the localisation of the recurrences in the three groups. Median time between initial surgery and recurrence was also almost the same in the three groups and 75% of the recurrences appeared within 2 years. Twenty percent of the patients in the primary surgery alone group, compared with 49% and 38% in the preoperative and postoperative irradiation groups, respectively, had distant metastases at the time of the diagnosis of local recurrence. The predominant symptom from the local recurrence was pain and, after treatment of the recurrence, pain relief was registered in 63%. In 66%, 16% and 22%, respectively, of the patients in the three groups, the intention of the treatment was curative, with either radiotherapy alone, radiotherapy combined with surgery or surgery alone. The 5-years-survival after recurrence was 6% in the primary surgery alone group and 0% in the other 2 groups. Of the 69 patients treated with a curative intention, 32% were locally symptom-free at death or the last follow-up. Our conclusion is that a local recurrence must be avoided due to the morbidity associated with local failure and the potentially low likelihood of curative treatment of a local recurrence.

The effect of systemic therapy on local-regional control in locally advanced breast cancer

One hundred and seven patients with locally advanced breast cancer were prospectively referred for multimodality treatment on protocol using chemohormonal therapy to maximal response followed by local treatment and maintenance therapy. Forty-eight patients (45%) were diagnosed with Stage IIIA disease, 46 (43%) with Stage IIIB inflammatory cancer, and 13 (12%) with Stage IIIB non-inflammatory disease. Induction therapy consisted of cyclophosphamide, doxorubicin, methotrexate, and 5-fluorouracil with hormonal synchronization using tamoxifen and conjugated estrogens. Local treatment was determined by response to chemotherapy. Patients with a clinical parital response underwent mastectomy followed by local-regional radiotherapy while patients with a clinical complete response were biopsied for pathologic correlation. Those with residual disease received mastectomy followed by radiotherapy while those with a pathologic complete response received radiation only to the intact breast and regional nodes. With a median follow-up of 64 months, patients with IIIA disease had a significantly lower local-regional failure rate compared to IIIB inflammatory patients, with the 5-year actuarial local-regional failure rate as only site of first failure 3% for IIIA disease versus 21% for IIIB inflammatory cancer (p = .02), and local-regional failure as any component of first failure 12% versus 36% (p = .01), respectively. When local-regional failure was analyzed by repeat biopsy, 5/31 (16%) patients with a pathologic complete response treated with radiation only developed a local-regional failure versus 2/53 (4%) with residual disease treated with mastectomy and postoperative radiotherapy. The 5-year actuarial local-regional failure rate as first site of failure was 23% for radiation only versus 5% for mastectomy and post-operative radiotherapy (p = .07). The response to chemotherapy did not reliably predict local-regional control. Both relapse-free survival and overall survival were significantly better for IIIA versus IIIB patients; stratification by repeat biopsy did not however, significantly affect either relapse-free or overall survival.